Obviously one should not always be happy. You shouldn't be happy at a funeral. You should also have cause to go to a funeral (having friends, family, etc.). You should also do things you might hate or cause pain because long term they are good. Studying, running, etc. Life if full of these struggles and they are good.
But there is also a common hedonistic misunderstanding where people seek pleasure, avoid pain, and think it will lead to happiness, or fulfillment, or however you want to characterize a "good" life. I see this a lot in the "self-care" advocates who justify unhealthy behavior by positioning it as championing some self-diagnosed mental health cause. It often looks like "I'm going to ignore my responsibilities because I feel bad and people shouldn't question me because I am the full authority on anything I categorize as my mental health."