the skill you added to future proof yourself. how did it actually age?

i spend a lot of time reading peoples profiles for work, and at some point i started keeping a rough tally of which listed skills i could actually picture the person using tomorrow.

the split was not where i expected it. the things that held up were almost never the named tools. they were phrasings like "took a vague problem and turned it into a spec someone else could build from" or "owned the incident nobody wanted to own." the things that aged worst were the specific tool names people added because job postings kept asking for them. a lot of those are now either gone or a checkbox you can clear in an afternoon.

the rule i think sits underneath it: a skill that was expensive because the tool was hard tends to expire. a skill that was expensive because the judgment was hard tends to hold. the first kind gets automated. the second kind gets amplified.

what i cannot tell is whether that actually generalizes or whether i am pattern matching on a narrow sample of the kind of profiles that end up in front of me.

so two questions.

what is a skill you deliberately added because you thought it would future proof you, and how did it actually age?

and the version i am more curious about: did something you picked up casually, with no strategy behind it at all, turn out to be the durable one instead?