It's no different than any other occupation. You're starting off at the very bottom of the totem pole and need to build a solid and very basic foundation before moving up in the ranks with time and experience. Going in blind (as I did) did not hurt me one bit, because they teach you what you need to know when you need to know it. Just be positive, open-minded and pay close attention to the officers (licensed) and cadet officers/upperclassmen as they guide you. A lot of stuff won't make sense initially, but there is plenty of time over the course of the first year to master the materials presented to you before 3rd class cruise.
I will say this though, some of what they throw at cadets in indoc now is rather pointless and a waste of time (lifeboat launching, for example) as they cover that in much greater detail later on. The focus used to be on learning how to follow orders, shipboard terminology, understanding the hierarchy of the regiment and training ship (and ships in general) and learning the very very basics of seamanship.
Would I do it all over? Hell no, but I wouldn't trade the experience for anything in the world.