I love how it categorizes skills into three buckets:
Learned skills, Acquiring new knowledge or polishing techniques. (Examples: Learning an instrument, programming.)
Confidence skills, Expanding your comfort zone. (Examples: Anything social public speaking, sales.)
Internal Skills: How you act and react. (Examples: discipline, dealing with negative emotions, ability to focus.)
And it summarizes to obtain these skills, we have to overcome the stress from learning, step outside of the comfort zone to grow confidence, and face adversities to grow internal skills.
Click on the link above and read the whole article, it's not too long but super useful. Especially in the "Atrophy" paragraph, it's the first time I hear someone describe things from that perspective.
Here is the very well made video from the author: