Fair question. I have often thought that sex was the ultimate motivator.
But the more I've gotten to know myself the more I've done things to please me. Would I still dress nicely and cut my hair, shave, etc? Most likely because I enjoy looking good.
I have started to wonder if claiming we do things "for ourselves" is always an honest statement. Some things surely are, such as taking care of your health because it makes you feel good and be more engaged in the world. Even volunteering at a soup kitchen can indeed be "for yourself" because it help you feel grateful and decrease self-absorption. But it seems like there are many cases where people won't admit to doing certain things out of a desire for social approval and status, even though it's evolutionary hardwired and perfectly natural to want it. For instance I suspect that the majority of men who get heavily into bodybuilding/aesthetics do so to impress other men or attract women, nothing more (and there's nothing wrong with that). And surely there are men who buy nice cars for the status,
even if they genuinely enjoy the car, to pretend it was 100% for "them" is hard to believe.
You can once again ask yourself any time you do a behavior, if you were the last man on earth, would you still do it? Do you really believe if someone was the last person on Earth (and was otherwise psychologically healthy), they would still maintain their hair/facial hair, dress sharp, and take care of their overall appearance? I'm not settled on this myself, but I see this "for myself" claim more and more (especially from women) and I am becoming increasingly skeptical.