It's subjective based on the check airman and especially your overall attitude/bearing.

For example, there are some peope who get all flustered in the "real" airplane on the line--typically the know-it-all types who are on APC giving advice to everyone before they even finish their checkride (cough cough, DeltaJuliet, cough cough).

Humility goes a very, very long way if you're an FNG in this industry--keep that in mind when you're on IOE--too many new hires these days think this is some kind of guaranteed thing they're entitlted to. Ironically, the new hires who seem to be the most humble and willing to listen & learn on IOE are the ones with a few thousand hours and a decent amount of 121 turbine experience--it takes time and experience to really comprehend how much you don't know, if that makes any sense.

Working the radios is a big hurdle for lots of people, especially people who haven't flown in and out of highly congested airspaces before--there's lots of slang and localized ways of doing/saying things, and it takes quite some time before you're really able to juggle ATC, comms with dispatch/maintenance, taxiing around and not having a runway incursion, all while keeping your eye on weather, fuel status, potential rest/FDP issues, etc..

This is why some of us on here kind of roll our eyes when people in this thread who are completely new to 121 flying confidently proclaim their ideations about upgrading in one year with exactly 1000 hours of 121 SIC time. IMHO you haven't seen enough stuff or developed enough instincts at that level, but maybe it works out for those "shoulder straps on always" type guys who have it all figured out!