You may be familiar with some of the research on the power of diversity in driving company performance: that more gender diverse leadership teams can lead to higher returns on equity, lower risk, greater customer focus, increased employee engagement and greater innovation.

And you may be able to see the logic behind the power of diversity: bringing together people who have different skillsets, backgrounds, experiences and perspectives enriches a team and can lead to better decision-making. (Put another way, it’s hard to build a national championship team if your players are all point guards.)

In my new book, Own It: The Power of Women at Work, I walk through some of the qualities that women bring to the workplace: qualities such as risk-awareness, relationship focus, ability to see problems holistically, learning orientation, long-term perspective, and focus on meaning and purpose. Pretty good characteristics, right? Ones that can make companies better, right? Ones that, I would argue, are becoming even more important as the pace of change in business increases.

So, why is so much of the business advice for women out there to…..well…..act like a man? Why have so many performance reviews that I have received over the course of my career pushed me in that direction?

Take a seat at the table. Project confidence. Get rid of the up-speak. Take on p&l roles instead of support functions. Raise your hand for jobs you don’t think you’re fully prepared for, because you know the guys are. Be more forceful.

In other words, conform to how the guys are acting.

This is despite the fact that the power of diversity in driving business results is……wait for it……diversity. It’s not bringing together a bunch of people of difference and training them to behave the same way.

So why the heck do we do this?

I believe it’s because we’ve been socialized on what leadership looks like: strong, certain, confident……male. I believe it’s because it’s easier (so, so much easier) for managers to manage everyone in one way and direct them to act in one way, rather than manage them as individuals. I believe it’s because the benefits that we hear about from diversity are so amorphous (“If I have more diverse individuals acting in diverse ways, my business’ ROE will be higher, in theory….Mmmmmmm….Never mind.”)

But the costs to this approach are real:

First is the cost for us as women. It’s just plain exhausting to act like something you’re not, day after day after day after day. (And, newsflash, there’s no guarantee that it even works; there’s an entire body of research that points to the backlash women professionals receive when we act too much like a man.) There’s no doubt that this pressure for women to act like something we’re not has driven any number of us out of business; I can’t tell you how many conversations I’ve had over the years with women who were throwing in the towel because they found it simply too exhausting.

Second is the cost to businesses. Yes, it’s a cost of not achieving the returns based on having that diversity. But it’s also the very real costs of having to find and train women’s replacements; these costs are calculated at up to 200% of her annual salary. Those are real dollars out the door.

Third is the opportunity cost of missing women as a market. You need go no further than my old industry, Wall Street and the investing industry, to see the impact. 86% of the industry’s financial advisors are male; the industry is built around the concepts of “outperforming,” “beating the market,” “picking winners;” and its brand symbol is a bull. All very male. The result? Women don’t invest as much as men do, and the industry is thus missing a significant source of business. (Even more importantly, this has had a negative financial impact on women in the past, since they haven’t been as fully invested as men and thus haven’t earned the historically greater returns in the markets.)

Fourth: At an extreme, homogeneity can lead to group think, which can cause industry “accidents.” Case in point: the financial crisis. Anyone really think it would have been as bad had the industry had more women and more people with different backgrounds??

I’ve worked at companies at which I felt like I couldn’t be myself, and I’ve worked at ones at which I could; and boy what a difference it made. At one company, I never “got” the politics; I felt like there was a secret code in which certain opinions were welcome and others (typically ones that dissented from the CEO….but not always…) were not. But I didn’t have the code book and so would come home at the end of the day drained.

In contrast, when I worked at Sanford Bernstein, that company celebrated intellectual diversity, and the management team relished a good debate. Everyone was allowed to be their full quirky selves. Is it a coincidence that it was there that we identified that equity research and investment banking were in fundamental conflict? As a result, we took ourselves out of the investment banking business before the early 2000s, when the industry became embroiled in the scandal for providing conflicted advice to research clients. I believe we were able to come to a better decision in this case because we were a diverse team intellectually, and the culture we had built meant that we didn’t need to edit our personalities and opinions.

(And before you decide that making a decision to exit a conflicted business is the luxury of smaller companies, it might be worth asking who earned a greater profit from 1998 to 2008: Bernstein or Merrill Lynch? The answer is Bernstein – because it didn’t’ suffer the big losses in the downturn. So it depends on how you define size.)

Ok, you may be saying, the idea of allowing people to act like themselves sounds like a good one. But what will make this happen now? The research has been around for awhile, and there have been plenty of opportunities to draw these conclusions. But not much has changed.

Here’s what is different going forward: women increasingly have other career options. We can tap into more information than ever before about the cultures and policies of companies at which we may want to work (or, for that matter, from which we may want to buy or in which we might want to invest). Additionally we are entering what I think could be the great age of female entrepreneurialism. As the costs of starting businesses come down, the support systems around entrepreneurs grows and an increasing number of successful female role models emerges, this career path moves from “nice to dream about” to a real option for more people.

As a result, women have more freedom and more options than we’ve ever had. Add to that that we control $5 trillion in investable assets in the US, jointly control another $6 trillion, direct half of consumer spending and make up half the workforce…..and that the existing power structure brought us the financial crisis…..given all that…..remind why we women are being told to act like men?

Going forward, we won’t. And it will be good for all of us.

Sallie Krawcheck is the CEO and Co-Founder of Ellevest, an innovative digital platform for women. She is Chair of Ellevate Network and the Pax Ellevate Global Women’s Index Fund. She is former CEO of Smith Barney and Merrill Lynch Wealth Management.