Yeah it's not mad shit like "Today I learned how to fly an F16 raptor" or anything like that. Like I spend about a half a day improving my german so I'll write down, "I now know words x, y, z in german" or when I go for a jog I'll write down "I ran x km in y minutes". I also do it for interesting facts I learned from watching tv or reading or whatever.
I dunno, I feel like it does a good of shaming myself out sitting down and doing fuck all every day. It also forces me to read/watch/play something new rather than falling into my comfort zone.
You know, this is actually a good idea. Stealing it.