It's not a matter of "painting over the difference". It's a matter of having standards set for my behavior that I was expected to maintain regardless of how I felt.
"I was expected to display patience whether I felt it or not." I can't display patience. I can display impatience, by twiddling my thumbs, for instance and I can be forbidden to do so. I can be told to wait. I can also be allowed to twiddle my thumbs while I wait.
I strongly suspect you mean the not twiddling kind of waiting.
Feeling angry, frustrated, selfish, impatient, annoyed and so on was all fine. Letting standards slip because I was feeling such ways was not.
I find that really confusing. I obey orders and follow rules because that's what I signed up for, no matter how I feel about it in a particular situation.
Sometimes I don't like it and that may even be the point of the exercise. In any case, my poker face is off limits.