If Achilles' had his heel, Ciro had his knee.
Then, just after arriving in France for Ecole Polytechnique, the boys were playing indoor soccer, and to impress the girls Ciro was playing really hard, even took off his shirt, and suddenly when he was running by himself his knee snapped, he fell and it hurt like hell.
Ciro was on crutches for a few weeks, but the inflammation went away, but then he tried to play more soccer, but the knee was not as stable as before, and once he tried to run full speed, it slipped and hurt him a bit more (less severely) and so he gave up. For some reason it was not visible on the tomography made at the hospital.
Maybe Ciro should have investigated more though, certainly an experienced doctor could have done a hand pressure exam to determine which joint was damaged manually even. That was a medical failure.
So from this day on Ciro gave up on all interesting sports, and confined himself to more repetitive stuff like gym weights and cycling: Section 184.108.40.206. "Ciro Santilli's sport practice". At Polytechnique he was forced to take up swimming as his mandatory sport, that was unbearably boring.
This defect is likely genetic since a close relative had similar problems.
But oh well, his then not-even girlfriend was impressed enough by the soccer or sorry enough for the sucker to marry him, so it worked out.