[tumblerz]

Learn any moderately complex system very well.

From past personal experience: get an old vehicle and make like new; learn linux on machine not best-suited to it; and, with out getting overly specific, gain skills by getting involved with people outside your milieu--volunteer, or get a side job that teaches you a useful skill via mentors with perspectives you do not normally encounter.

In my experience, learning a complicated system translates well to another.

Finally, and perhaps this will sound a bit life-coachy--sorry: learn to suffer, dynamically. Learn that your limits are often imagined, and that you can "put away" unpleasant feelings in order to perform adaptively within, or even enjoy, struggle. This a skill of mine that not many people have. It's probably not crucial, as people without it seem to function fine, but it does afford me unique opportunities.

[Dowwie]

Endurance is absolutely a great life skill. We can do so much more than we think we can when we learn how to manage our thoughts. It is what enables people to become navy seals, cardiologists, pioneers in one's field, or all of the above if you are Jonny Kim. Jonny spoke at great length on Jocko Willink's podcast if you are interested in his story of personal triumph: https://www.youtube.com/watch?v=yujP3-AxXsI