Comment by pempem
Such a good question - I hope someone answers with more than an anecdote (which is all I can provide) - I've found the skills that don't leave you like riding a bike, swimming, cooking are all physical skills. Tangible.
The skills that leave: arguments, analysis, language, creativity often seem abstract and primarily if not exclusively sourced in our minds
Google "procedural memory". Procedural memory is more resistant to forgetting than other types of memory.