people are intimidated by the reference class of "hand tools" and so might fail to effectively use even the most basic ones.
You'd also be surprised how many people fail at basic physics (the longer the lever the more force you can transmit, so don't hold the wrench in the center). I've seen people fail to correctly use screwdrivers, wrenches, pliers, etc.
So, transferable skills: skills that, upon improvement, increase your ability in other areas (and also improve other, higher-level skills).
A basic example would be reading/writing. Knowing how to read and write allows one to access a huge amount of other skills and resources which are otherwise unavailable. A less obvious example would be clear speech (enunciation). Ability to speak clearly improves one's prospects in a lot of different areas (e.g. professional advancement, dating, etc.).
I'm looking for additional examples. Which skills did you find to be most transferable? Did you become proficient in X, and then found this helped you in many other areas of your life? Please share.
(I tried to find whether this was discussed before, and failed; if it was, I would appreciate the link.)