Here I am performing a squat while holding my phone.
I'm doing a squat (one of about 120 today) because I'm trying to 'get fit'. Getting fit seems to involve doing things that hurt. Doing 120 squats did, in fact, hurt. I also perform a number of other hurty activities, including press-ups, sit-ups, leg raises and 'the plank' (which *really* hurts).
After doing this for a few weeks I can now do more of these activities than I could at the start, so perhaps I am getting fit.
So, why does it still hurt?