I thought Bojan would have been one of the worlds best players in 2013 to be honest, he was amazing for a 17 year old, like just crazy good, not Messi, but not far off and he was playing in a squad which had a cesspool of problems, egos, partying, lack of care etc. And it seemed only natural that he'd flourish under better management. I think a lot of his confidence issues are down to that easy headed chance he missed vs Inter and the disallowed goal, he seemed to drop almost instantly after that, I suppose for a young player with fragile confidence those misses will really mess with your head.
Look at the difference between Bojan and someone who looks naturally confident in his game, like Tello, he missed a few chances vs Madrid last season and that could have really set him back because we lost the game and the league, but he seems to have moved past it and he's actually played quite well this season when given the chance.
I think Alexis and Cesc are in the same mould as Bojan and they let the big misses get to them and they refuse to take a chance and shoot because they hate that feeling.
Tello is more like Messi, after his penalty miss vs Chelsea you wouldnt have been surprised if he never took a penalty again (Like Bergkamp) but he still takes them and he's got the confidence and belief in his own ability to keep going and then try and make up for and not let it affect him.