If a friendship that was once fun is now work, say goodbye.
If a cause you once cared about no longer makes you feel passionate, find a new one.
If a job makes you feel depressed rather than happy, quit.
At the end of the day, it really is that simple. Forget the responsibility you feel to anyone else because the only responsibility you have is to yourself.
I certainly have a tendency to hold onto things.
Like, because a friendship is old and was once valuable to me, it means I need to keep it in my life. It's called the sunk-cost fallacy:
Reasoning that further investment is warranted on the fact that the resources already invested will be lost otherwise, not taking into consideration the overall losses involved in further investment.
On the topic of work: when Sunday comes and you're dreading the work week ahead of you in a way that is all-consuming, it's probably time to find a new job. People have a way of making themselves believe they're "happy enough". You tell yourself, "My job isn't all that bad. The pay is okay, the hours are good, vacation is decent." We find a way to live with situations that don't make us happy by convincing ourselves that it's not that bad. We feel loyalty to companies that feel no loyalty to us. We feel we've worked somewhere for so long that it would be silly to give up the "perks" we have to start somewhere new. But that's bullshit.
These days, I try to only do things that I want to do, and things that will make me happy. And you know what's happened?
I'm now happy... for the most part.