The best analogy that I have heard to describe medical school is the pancake analogy (not my idea, credit should go to whoever first came up with this)
As a medical student, you have to eat 5 pancakes a day. Now 5 pancakes is doable, and almost anyone can do it. But you have to eat 5 pancakes every day. And if you only eat 3, or 4 instead of 5, the "leftover" gets added to the next day's stack - so you will have to eat 6-7 pancakes the following day. Skip a day, and you will have 10 pancakes the next day to eat. Skip a few days in a row, then you are really behind, with a stack of pancakes to conquer.
When you start, you are eager, hungry, and devour the pancakes without problem. But with pancakes every day, and the need to keep up with the pancakes so you don't get overwhelmed, it slows you down, little by little, until it becomes a chore to get through the pancakes (but they are necessary, since you can't go to the next step without finishing all the pancakes, with the rewards being more pancakes per day