(Fish doesn't make me 3x more productive, but...) I think a good analogy would be having sharp tools. If you don't have to exert yourself to do simple things, then menial tasks use less mental energy which you can save for your actual work.

Fish manages to pull this off without _any_ configuration burden (I use it completely stock), which is exciting because usually to benefit from shortcuts or macros or other "productivity hacks" you have to become a power user.