The recency of the good feelings matters too. If you push back now and set expectations for everyone, then a year from now your boss will probably remember the consistency more than the push-back.
Of course, it will depend on the people involved.
Communicating honestly (“If we need that done today, we have to deprioritize something else to make time”) will get you further unless you’re dealing with very immature management.
Any employer that does this is toxic. You should find a new place to work. One of the hardest and most important professional soft skills is knowing when to say no and setting proper boundaries.
if somebody is butthurt because you refused to take on more than you are able to... that's a bad spot to be in no matter if you refuse or not.
Okay, but…if you work a job not for fun but because you need the money, then you’re still better off in the bad spot with a job than the bad spot without a job.
I can understand if this is the first time it happens, but some people still complain about this after 5 years of dealing with the same thing.
At that point it’s their own fault.
If you happen to have access to free food, shelter, etc. and were only holding a job for fun, then sure!
Maya Angelou has a quote that's supposed to be inspirational but is actually depressing as hell: "People will forget what you did, people will forget what you said, but they'll never forget how you made them feel." Want to actually succeed in the actual real world and not the fantasy world internet commenters exist in? Focus on making people feel, not on results. If you say "no", they'll remember you made them feel like the person who turned them away when they needed you most. If you just say yes to everything and get to what you can get to, you'll make them feel like the person who tried their best.
Until all of civilization starts rewarding actual results over vague feelings (it never has), focus on appearances.