I haven't been as diligent with my guitar practice recently, and in particular I've been avoiding the exercises where you have to do fast chord changes. I found it very difficult to get my fingers into the correct arrangement in time. But today I was determined to master it. I did the same exercise over and over (the chord order is random so you can't anticipate what will come next), way past when my fingers were hurting really badly. And finally I got my perfect gold star score!
Now I have lines of blood under the skin on the tips of a couple of fingers. Ouch.