Since we talk resizing windows, for months I was _sometimes_ unable to resize windows at all, and couldn't figure out why. I thought it was a random bug of macOS.
Finally I realized the issue: if a window spans across two displays, it won't resize. Insane!
(I have an external monitor up, laptop down, and it's easy to move a window such that it stretches a few pixels from monitor to the laptop. No resize for you!)