I really struggle with this and have yet to have the "click". I feel maybe I've been doing a bit better as I've gotten older (32 now), but still nowhere close where I want to be - both in terms of mentally letting go and objectively where I want to end up.
The problem I really struggle with is the dichotomy of the two in my head. One part of me wants to be a "success". Professionally for me the score is kept with money. If it's in terms of my hobbies/other pursuits it's becoming somewhat known in those fields.
However mentally success for me means being content...which contradicts those things in most ways and in my head they act as the destination for being content.
If anyone has any advice on how you've managed this I'd greatly appreciate hearing about it