Being lazy
I almost exclusively use Python for my job and have been eye-balls deep in it for almost 5 years but I really lack in-depth knowledge of builtins.
I recently learned of an awesome builtin called calendar that has way more than I know about for sure but I'm glad I know it's here now!
I only needed it because I was too lazy to hard code the 7 weekdays into my module but it turns out there's a lot of useful things like calendar.isleap()!
Future use
I'm not exactly sure what will come my way where calendar will be super relevant but like anything, I'm just glad to know it exists for when the time arises!