Recently I was going about my business when suddenly..
...my calf decided to secede from the rest of my leg. Unfortunately for me (and my calf) that plan wasn't going to work because, you know, there's connective tissue and stuff in there. Ultimately, what I thought to be the most terrible charlie horse turned out to be in actuality a torn muscle. Not knowing this at the time and still believing myself to be invincible (like you do), I continued to stretch and walk about on the horrible lake of fire that was my leg.
Don't do that, kids. It'll just make things worse.