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You probably don’t want to be known around the office as the one who’s never willing to lend a hand to a colleague — being pals with your co-workers, after all, can make it easier to get through the day — but there’s a downside to being too giving of your energy: It can actually make you worse at your job.

It’s a fine line to walk: On the one hand, as Wharton researchers Adam Grant and Reb Rebele noted in a recent column in Harvard Business Review, research has shown that people categorized as “givers” — as opposed to “selfish ‘takers’ or quid pro quo ‘matchers’” — typically make for the most valuable employees, sharing their time and knowledge in a way that elevates the workings of the whole group. On the other hand, givers are “also at the greatest risk for burnout,” they wrote. “When they don’t protect themselves, their investments in others can cause them to feel overloaded and fatigued, fall behind on their work goals, and face more stress and conflict at home.”

But, the researchers argued, there’s a way to be a giver while simultaneously avoiding “generosity burnout” — the key lies in knowing that generosity and selflessness are not one and the same. “Being an effective giver isn’t about dropping everything every time for every person,” they wrote. “It’s about making sure that the benefits of helping others outweigh the costs to you.”

Think of it this way: Let’s say you’re crashing on a looming deadline for some super-important project when a colleague asks for your help fixing the copy machine. The selfless thing to do would be to get up from your desk and go help him out — but that would also be a foolish use of your time. In this case, the cost of your missing your deadline outweighs the cost of him having to wait a little longer to scan something.

Or, to borrow from Grant and Rebele’s example, let’s say you’ve agreed to set aside time to teach something to a colleague, and they’ve just asked if you wouldn’t mind doing the same for one of their buddies. It might be selfless to set aside another chunk of time to repeat the lesson — but, again, it would also be something other than the best use of your time. A better move would be rescheduling for a time when both people can make it, allowing you to combine two lessons into one. “Finding ways to give without depleting your time and energy,” they wrote, “is generous but not selfless.” The best way to maintain your generosity over time, in other words, is to make sure you’re a little bit selfish, too.