Hi !
Basically, ug neet to to get into mbbs so if that happens at first attempt then great, else if a person is hell bent on doing mbbs only, he or she will keep trying. Some may have a back up plan, some go for other degrees. So you have options wrt your career there. Also there are a decent number of ug seats so not many go disappointed.
Coming to pg preparation, its 19 subjects, thought of which can be daunting but its what one has studied for 5.5 years. But the frustration creeps in due to the fact that you have a degree,but no one gives it the respect it should get. Youre not financially stable as an individual. Also now, whether or not one is able to crack pg, there is no going back, no alternative as this is only what you can do . In comparison to the number of ug seats, pg seats are very less so every year while the competition is rising, many students go home empty handed or are forced to take specialities the have no intrest in.Im not saying pg prep is difficult, I feel its easier than ug prep, but its easier for those who overcome these mental hurdles earlier at each stage.