You're right, but just to point out the obvious - you can decide (to some extent) not to be bitter, even if you aren't fulfilled at your job.
Many people, in fact most people, and certainly most people throughout history, have worked not because it was the thing they wanted to do to be most fulfilled. They worked because they had to provide for their family.
The choice isn't binary - it's not "do something you love and not be bitter" vs "work to provide and be bitter". You can also choose "work to provide, understand the tradeoff you're making, and accept it". You can still have a plenty fulfilling life outside of your job - many people do.
Many people, in fact most people, and certainly most people throughout history, have worked not because it was the thing they wanted to do to be most fulfilled. They worked because they had to provide for their family.
The choice isn't binary - it's not "do something you love and not be bitter" vs "work to provide and be bitter". You can also choose "work to provide, understand the tradeoff you're making, and accept it". You can still have a plenty fulfilling life outside of your job - many people do.