The energy that they take is your life energy and it can definitely take its toll if you let them take too much. It’s not a willpower thing either. I consider myself to be someone with a decent amount of willpower, however, the question of willpower becomes kind of meaningless when you have to use the same amount of willpower that you’ve used to do a set of squats in the gym for example, just to get out of bed… And that’s what can happen if your life force is diminished.