News flash: that's the case for the majority of the background/experience check items that they're asking for you to report on your application. It is an integrity check (just to see if you'll self-report) just as much as it is a survey of your background.
Almost everyone flying at the airlines has a black mark on their record of some sort, but we in the flying business don't generally share the skeletons in our closet with even our friends, so we tend to have a distorted view of who exactly our peers are. Plenty of high-performing pilots and officers have made mistakes that left a mark on their otherwise-excellent careers.
A lot of guys have busted checkrides, but that also goes for even more significant issues like administrative punishments, Art 15s or LORs, and -gasp- even FEBs -- a lot of things that we consider the kiss of death inside the USAF fishbowl but don't carry the same perceptual value in the civilian flying world.
Some of the black marks would make your eyes pop out: DUIs, crashed airplanes in which the cause was pilot error, even criminal records. Hell, at FedEx there was a dude who had been arrested and charged with murdering his wife.
Just remember they're looking at the totality of your professional experience, and they don't expect that everyone walking through the door is going to have a perfectly clean history.