What skills are worth obsessive focus for an unshakable future?

I’m at a point where I’m willing to commit completely to mastering one skill — even if it means sacrificing balance temporarily (long hours, minimal rest, limited social life).

I’m looking for skills where deep, obsessive focus can lead to an unshakable and sustainable future — financially, intellectually, or in terms of independence.

If you were starting over today with this mindset, what would you master? Bonus points for sharing books, lectures, or structured learning paths that helped you get there.