The less I take myself seriously, the more I apply self-compassion, and the less I let my performance/failures define my sense of self, the happier and less stressed I am.

I discovered this by accident. I used to be the opposite: my self-image used to be relatively inflated, and my sense of self was tightly integrated with external events. When those external events turned south hard enough to totally shatter my ego, it felt like my brain -- utterly against my will -- decided, "I guess we gotta let go of caring about stuff this hard." I ceased to be able to care as hard (seemingly permanently). I've been happier and chiller ever since. :p