I mean I think the bigger issue is that, at least for me, unless I am regularly using a skill I learn I forget most if not all of it.

I trig, and calc 1 yet I hardly remember how to solve most problems because its not something I use regularly.

Same with subnetting or remembering certain programming languages.

I literally don't use these things 99% of the time and so I forget them. Sure I understand some of the basics and I could probably pick it back up way faster than someone who knows nothing but I am human.