Humans have a tendency to do something in repetition, may be a small or big gesture, when we are exposed to extreme situations. The Professor tapping his glasses when he would get nervous or some part of the plan went wrong or something would have happened which wasn’t supposed to!
The Professor had fallen for his own trap. The ear’s ability to elicit paranoia. That’s the card Sierra had played to destroy us. Then, it was war. La Casa de Papel: Part 3 (2019)
It would have been easier if nothing had happened, Raquel. You were the only flaw of a perfect plan. A plan that was perfect but it isn’t anymore. You know why? Because even if it all goes well I will be fucked cause I won’t be able to see you again. Do you think I entended to fall in love with the head of the case?