I’m selective about what I learn by only one measure... is it fun for me? Usually it turns out to be not only fun, but also intellectually stimulating and bring

I’m selective about what I learn by only one measure... is it fun for me? Usually it turns out to be not only fun, but also intellectually stimulating and brings new ideas in front of me. However over time I’d say nothing I learned on the side was of no value to my day job and to my overall development as a programmer.