Okay, you've been working out hard, feeling tired, worn out, beat up. You are suffering through the work outs and somehow you're still here and one day you stop to notice, I'm not sore today.
That's the crux. You're no longer sore, you're now past all the hardest stuff. It's all results from here on out. This is the worst time to stop because you've finally arrived at the other side, you're finally getting in shape.