On the rationality of expressing gratitude
If you have a better option, there’s no reason to complain. If you don’t have a better option, it makes no sense to complain.
Complain if you must, just don’t pretend it to be a rational thing to do. Complain doesn’t help you to solve your problem, and it annoys people who listen to you complaining.
Even if you don’t feel grateful, express gratitude. Speak, write, think. You can always, always express gratitude no matter how awful you feel. No, it’s not easy, but it’s never impossible. Ever.