Used to be deadlifts as I plateaued for ages. It was just a grind where I wasn't progressing. I finally started to use straps and everything clicked (in a good way). Started to enjoy them more, so I did them more often and they become one of the favourite exercises.
Then it used to be squats, like what stringers said. Got the right shoes and technique advice, and now they feel better and I look forward to them.