For me, self-design is about DIY.
I like to make things for myself, and to be able to make those things I need to learn new skills and techniques. The things I make are very specific to my needs and interests, and in a way they also change me and and become part of my personality.
I learn mostly through my self-projects. Because of my ADHD I am rarely able to watch a tutorial from A to B.
I also copy/DIY things because the originals are to expensive and to better suit them to my needs, like synthesizers. Or because they don’t exist yet, like the skates.