Learning to play the guitar will not get you a better handstand.

That would be the logical conclusion for anyone who doesn’t examine the case very closely, and there’s really no incentive to examine the case closely.

Yet, when you examine the case closely, it turns out that stronger fingers from holding chords on the neck of the guitar are also stronger when they need to hold a handstand position, digging the fingertips into the ground to balance. So learning to play the guitar will actually get you a better handstand.

You’d never spot the synergy unless you happen to try both, and you’d never think of that skill transfer as an active development choice.

This happens a lot! Skill transfer might be physical, but could just as easily be about thinking patterns, emotional flexibility, or something completely different.

Writing a task down with a checkbox next to it makes it far more likely that you’ll get the task done.
If you practice flow-writing, you get better at organising your thoughts.
But those don’t make a lot of sense until you try them out and see for yourself.
Doing a ton of core-training helps your singing skills. And that works inversely too!

There’s so much spillover between learning from different activities that the only conclusion that’s truly viable is to do lots of things, and see what stacks.