Training takes time obviously. But how in some fictional stories I see characters amassing a lot of skill way too quickly. For example, in Disney’s Mulan, she failed in her all training and was sent home. But instead of leaving, apparently she trained overnight and the next morning completely wowed everyone with one accomplishment. The next few training clips, which can’t be too much time, shows her being the best at everything . Uhh like how??!!
Through the miracle of non-linear time.
For a good writer, the montage, or time skip can be useful to keep the story moving. It can bypass lots of repetitive text, or just ignore mundane elements that wouldn’t make the story interesting. If it’s not relevant to the story, or doesn’t advance the characters, you don’t need to show your character eating. There’s no reason to include the scene.
Training is a lot like this. You may want to include examples of their training, and specific lessons, but if someone was practicing the same technique for months, gradually improving, that’s not going to be interesting in detail. You only need to show the overall change.
If you have moments where something significant happens, that’s worth dwelling on. Your character comes to a new realization, they achieve something they’ve been working towards. When a lesson is important for the story, either as foreshadowing, for world building, or as character development, that should be included. When it’s just that your character doing the same thing they did yesterday, you don’t need that.
The problem is, training montages can easily turn into an ill-defined, “level up” session. Central to this is that the author exists outside of time for their story. They know the future, and have absolute control of how it will flow on the page (or screen.) This can lead to cases where the character’s training montage isn’t actually compressing time, and characters are simply gaining skill at an impossible rate.
The related problem is that you can have an extended time skip, but don’t cue the audience into this at all. I think this is what we’re supposed to take away from Mulan. She’s been training for awhile, but it’s not clear that there’s a time jump. The Empire Strikes Back has a similar issue. It’s unclear how long Luke trains on Dagobah, and it’s also unclear how long the Falcon‘s crew are on Cloud City. Both happen at the same time, and there some time skips, but it’s impossible to tell if Luke is training for hours or months. (We know it’s not years, because of the official timeline.) This is the kind of thing that could easily be addressed by showing a changing of the seasons, showing minor injuries healing, showing hair growth or even just kludging it by slapping a date slugline on everything or having a character remark about how long this has been going on.
I’m not opposed to montages per se, but I have seen them misused many times. It is extremely important for your audience to be able to understand that you just compacted four years of training into into a short sequence.
It’s also worth remembering that just because you’re pushing fast-forward for your main character, the rest of the world shouldn’t freeze up and wait. If you wanted them to walk away from their life and study esoteric secrets at a monastery for seven years to beat a villain, that villain’s plot should be fully realized and executed by the time they get back. Also it’s possible (read: this will happen) that their friends will be a little upset given they scampered off instead of helping.
There’s probably a punchline to be had in a “hero” who went off to engage in a training montage, only to discover that their original foe was defeated in their absence.
So, how does this work? It’s presentation. You’re informing your audience that your character spent time training, without going into excessive detail. It only becomes a problem when you sit back and go, “wait, what happened?”