At the end of the day, Thornton is an anomaly. He's one of the few guys who had the physical skills and, honestly, was not a good player out of the gate. He was too small, and he also wasn't as strong as he needed to be.
But rather than quit after failing repeatedly, he kept going. It's been that perseverance that's seen him now flourish under a team that's obviously offense-centric and has a high-caliber player in Mahomes that has helped him be successful. The Chiefs had the luxury of putting him on their practice squad and developing him. The Patriots were a bad team, and desperation ended up taking priority over patience. That and I don't know what KC's receiver coaches are like, but I feel like that also might have helped him. Along with whatever strength program he continues to be on, because he looks like a stronger player.
We can all talk bad about him, but this is one of those times you just have to give it to the guy. He could have just quit and listened to the doubters. But he didn't, and good for him that he's had the success he's had. He's worked hard, and he's earned it.