When I first began researching my book Stepmonster six years into marrying a man with kids from a previous partnership, one fact hit me square in the forehead: over and over, people with stepparents who heard about my project let me know that they liked their stepdads just fine. In fact, in many cases, they loved them, even considered them "another dad." It was their stepmoms who were the problem, they insisted. As one woman in her 30s told me, "I know it's not about me, because I love my stepdad. He's a great guy. My stepmother on the other hand—I can't stand her."

This theme—nice stepdad, "horrible" stepmom—was remarkably common, as was the tendency to consider a stepfather "another parent" but a stepmother more like "my father's wife," even when the relationship between the stepchild of any age and the stepmother was good. Most notable—and sad—was the marked frequency of strained relations between stepdaughters and stepmothers. Indeed, much of the literature on stepparenting suggests that, broadly speaking, stepmothers and stepchildren are less close than stepfathers and stepchildren. What accounts for these differences?

The common take on tensions between stepmothers and stepchildren in our culture is, of course, that stepmothers are overwhelmingly likely to be nasty, petty, and , creatures right out of the Brothers Grimm. It would only follow, this cultural logic goes, that their stepkids dislike and reject them.

The demographic reality—there are now more stepfamilies than first families in the U.S.—has gone some distance to close the gap between our perceptions of stepmothers as a group, and who they actually are. We know from the research, for example, that my own findings exemplify some important truths about stepfamily life: that many stepmothers actually bend over backwards to try to win over wary stepkids, and that most women who take on life with a man with kids of any age do so with the best intentions. As stepfamilies become statistically normative, we have the opportunity to re-write the stepmothering script along lines that are less fantastical and rooted in myth, and more rooted in the day-to-day realities of stepfamily life.

But that's just the problem. For it turns out that the root of much of the tension between stepmothers and stepchildren is in lived experience, not just in myth. This is particularly true in the case of stepmothers and stepdaughters. As it turns out, it's not just that most women with stepchildren try hard, at least initially. It's that they feel they have to, because they face significant challenges that a stepfather doesn't. The next time you hear a child, young adult, or adult talking about not getting along with his or her stepmother, you can bet one of the following challenges unique to stepmothers is at play:

1. Children, young adults, and adults have a harder time accepting a stepmother than they do a stepfather. This frequently translates into hostile and rejecting behavior. Simply put, the literature on stepparenting bears out the reality that stepmothers generally have a tougher row to hoe than do stepdads, and much of this difficulty steps from feeling rejected by and actually being rejected by their stepchildren of any age.

2. What makes it harder for a stepchild to accept a stepmother? What builds a stepchild's resentment of "dad's new wife"? If you think it's her own wickedness of just plain lack of trying, guess again. It may have more to do with the children's mother than anything the stepmother is doing or not doing. According to researchers including Mavis Hetherington and Constance Ahrons, after a divorce women experience more resentment and , and experience it for longer, than do men, who are more likely to nurture of reconciliation and work for "smooth sailing" with an ex-spouse. Based on her 30-year Virginia Longitudinal Study of life post-divorce, Hetherington concludes that stepmothers are frequently singled out for very bad treatment indeed by stepchildren who pick up on their mother's anger and resentment and become her proxy in their father's household. As more than one adult stepchild told me, "My mom wouldn't like it if my stepmom and I were close." Often, a stepchild who "hates" her stepmom feels that in doing so she is expressing solidarity with her mother. If mom would explicitly give her permission to like her stepmother, and let her know that being nasty to stepmom is not an option, the behavior, and the resentment it stems from, would likely vanish.

3. Women with stepchildren are more likely to feel compelled to try everything to win his kids over. This too often includes trying to act maternal and loving. And for a child or adult child in a loyalty bind—sensing that liking stepmom is a betrayal of mom—stepmom's overreaching and attempts "to act like she's my mom" will seem especially offensive and threatening. Thus she will be more roundly rejected. Stepfathers, on the other hand, have a wider berth to step back and let things develop on their own with their stepkids. As one man with a stepson told me, "I wanted my wife to be a mother to my son. I even thought it should come to her 'naturally' somehow. But I didn't feel the pressure to be that to my stepsons. They already had a dad and I was clear about that. I was there to be someone extra to do things with them, listen to them, stuff like that." Such double standards break against stepmothers. But with less pressure on them to be "paternal," stepfathers feel less pressure to act just like dads, and stepkids feel less internal conflict about "betraying" dad. Don't forget that having an ex-husband is, statistically speaking, generally easier than having an ex-wife owing to differences (again, broadly speaking) in anger and resentment post-divorce. Since dad is less likely to have a strong agenda about how his kids are "raised" by stepdad (who isn't as likely to feel compelled to do the raising anyway), there are fewer opportunities for conflicts between men across households than there are between women across households. All this contributes to the stepfamily mix, making it more combustible in the case of a stepmother household (husband, wife, and his kids) than in the case of a stepfather household (husband, wife, and her kids).

4. Girls, young women, and adult women, in particular, are likely to model their mother's feelings and behaviors and subscribe to her beliefs regarding her divorce from their father. This fact, plus the fact of an ex-wife's resentment of her husband re-partnering, often fuels the fire of a stepdaughter's hostility toward her stepmother.

5. and re-partnered or remarried fathers often feel fearful of incurring the anger of their ex-wives ("If she gets mad, I might never see my kids again") and of alienating their children if they say "no" or hold the kids to a high standard of behavior. For these reasons, an ex-wife may be a very powerful presence in her ex-husband's home, her agenda profoundly felt. And Dad's house may become the "no rules" household-meaning there are few rules about treating stepmom with respect, both because he is fearful of alienating his kids, and because of his ex-wife's influence. When a wife or partner with stepchildren attempts to assert her right to being treated fairly in the household under these conditions, her husband or partner may not support her position. This causes tension within the couple—tension that the stepmother may attribute to the stepchildren alone. And so the tension between stepmother and stepchild is further fueled, this time from within the stepparent/stepchild dyad.

6. In spite of increasingly involved dads, mothers are more likely to be awarded full or primary custody in most states according to divorce and custody experts. This means stepmothers are still likely to see their stepchildren exclusively on alternate weekends, holidays, and on vacations. Experts tell us it is harder to build a secure and happy relationship with a stepchild of any age in such "spurts." Stepdads, on the other hands, are likely to live with women who have custody of their children, facilitating daily interaction and a relationship that develops over time rather than in rushed weekends or potentially holiday "visits."

In general, therapists and the rest of us should be aware that, when an accusation of "stepmonster" is leveled, something far more complicated (and common) than a "wicked stepmother" is almost always the root cause. We should also bear in mind that rather than being a question of having "good intentions and a good heart," a stepmother's success with her partner's kids usually hinges on factors (outlined above) beyond her control.