Just like a casual fan who watches MMA cannot possibly replicate the moves they see on TV, a casual BJJ practitioner who sees a move once will be unable to truly understand how to make the move work. One reason for this is that in order to get a move to work well, one needs the timing and understanding of the inner workings of that move. A deeper look at this will indicate that it is far less important to learn moves than it is to learn concepts, as moves can fail us in a given moment, but the concepts which drive them are usually absolute.
An easy example of a move that is concept driven is the escape from bottom side control. A simple guard recovery requires the person on bottom to escape their hips and then replace their hips with their legs. This move is easy enough that people can learn it on their first day, but can take years to truly master. The pertinent question that a person needs to ask is why the move works? What makes it effective?
The concept of this simple movement is that if there is space between you and the other person you can fill that space with more effective and stronger parts of yourself, like your legs. The move itself is easy to learn, the concept of creating space and then dictating what goes into that space is far more difficult.
Another simple set of moves are attacks from inside the closed guard. These are some of the first submissions we learn. The triangle and the arm bar both feed off of the same concept: isolating a single limb of the person in the guard and attacking that limb with all four of the limbs of the guard player. This is a very difficult concept to master because it requires a tremendous amount of dexterity and timing.
The concept of limb isolation is central to Jiu Jitsu as it is what allows a smaller person to attack a bigger person. A bigger person may have a stronger arm or leg than a smaller person, but the entire body of the smaller person is invariably going to be stronger than a single limb of the bigger person.
What does all this mean?
Learning cool moves is fine and dandy, but it is about as effective as watching YouTube videos and then trying what you saw with your friends. In order to truly understand a move and make it part of your repertoire, learn what makes the move work, deconstruct the move, figure out how to break the move and what to do when the move is broken.
Concepts are far more powerful than moves, and you should spend more time learning about the inner workings of moves than you do learning new ones.