It's all about the mind
Your mind will quit well before your body!
250 Consecutive Kettlebell Swings With a 55# KB...
Brain: 50 reps. Ok, stop.
Body: You got this!
Brain: 100 reps. Ok, that's enough.
Body: You got this!
Brain: 150 reps. You're done. Your forearms are on fire!
Body: You got this!
Brain: 200 reps. This REALLY hurts. Put the KB down!
Body: You got this!
Baby: *Waking up from nap*
Body: Ok, you're done...
(Maybe. MAYBE I could have gone to 300.)