Sorry, I should have been more specific and said " I don't think anyone can constantly be intimately/romantically rejected and be totally unaffected emotionally".
It's not about being completely unaffected, it's about suffering, coming to terms with your loss, and moving on the best you can.
1- Try and battle through it and find a way
2- Make peace with being single and put your mind of it
I think you're all vastly overestimating the extent to which PUAs are affected by rejection.
A PUA being rejected by a woman they approach is not a comparable experience to a typical serially monogamous guy being rejected by a woman they attempt to pursue romantically. Their objectives are different, their motivations are different, their experience with such things is different.
A serial monogamist will approach some coworker he finds attractive and has gotten to know for a little while, and he'll feel somewhat upset about rejection because he will have become attracted to the specific person he approaches and will have daydreamed about possible romantic experiences with that specific person. A PUA's only criteria is "is that girl sexually attractive to me?," they view their targets as marks instead of unique people with individual personalities, their intent is to manipulate interactions in order to get the mark to sleep with them, and they have no intention of any longer term relationship than a fuck and chuck. If they fail with one woman, any other that looks good enough will do just as well.
PUAs are sleazy and maladjusted but they aren't too stupid to be aware that everyone has different sexual preferences. They have to be aware of this, simply by virtue of actively engaging with such things on a regular basis. Nobody will be physically attractive to everyone, not everyone will be in to casual sex, not everyone is available for sexual engagements, etc. There are all sorts of (actually legitimate) rationalizations they can come up with for why women wouldn't want to have sex with them, that aren't their fault. It doesn't have to be taken personally.
For a PUA, being rejected by a potential sexual partner is psychologically closer to how a salesperson feels when a client declines an offer than how a serial monogamist feels when a potential romantic partner turns them down.