A couple things from my personal experience.
A) People have varying degrees of susceptibility. I wrestled for about 11 years before my ears showed and I never wore headgear except to matches. Others got it in their first year.
B) Proper care can fix it after the fact but not always. I had my ear drained 5 times in a week and woke up every morning with it worse. Eventually, I had plastic surgery to fix it as it covered about half my right ear.
C) That shit hurts when it is developing. Once it hardens, you don't even know its there but when it is still soft, it is quite unpleasant.
D) Headgear helps but is not 100% effective at prevention. I've seen people who never drilled without them with mangled ears.
“If [Junior dos Santos] punched me as hard as he just punched [Mark Hunt] I would poop my pants.”