Anybody can fill 100 pages in screenplay format and call it done. Trained moneys could hit the keys enough times to generate a 300 page novel. Just because it's long doesn't mean it's done or right. There's a general confusion as to what a full-length story is and the truth is page numbers are only a symptom of something deeper.

Character Does Not Win Easily Or Quit

Stories of shorter length will be thus because they aren't as impactful as longer stories. They aren't lesser in impact due to length alone, rather what within those pages is said about a character. I don't think it says a lot about me that I once played sports and quit playing them, lots of people have done that. What speaks better to who I am is what I've gone through in my pursuit of writing. It's more telling what a character does to the extreme to gain something important rather than the steps that led them to know what that goal is. The stories of things I used to do that led me to writing are important, but not as crucial for knowing who I am as the journey I'm on now to be a writer; which will need length to fully flesh out.

Not Same Situations With Minimal Changes

If a long piece is filled with scene after scene of situations that aren't really too different from the one before, you may be putting together a thematically-related short story collection. If this is a screenplay you might be making a short film collection. It will still be called a novel or film, but it won't be using the form to its highest capacity. Situations in a full-length work won't be the same each time only different. They will grow out of what happened the scene before and they will escalate toward a climax or resolution of some sort.

Higher Stakes, More Severe Consequences

As scenes in your work progress, the escalation is in what is at stake for the character. Instead of a series of scenes where a character tries a bunch of different ice cream flavors, maybe each successive one he tastes has more and more of a chance that his blood sugar will put him into a diabetic coma. Now that says a lot that someone likes ice cream that much. In the pursuit of a goal the character won't just meet with a series of obstacles that aren't too much harder than the ones before, each successive scene should be more difficult and the consequences of failure more dire.

Demands More From Characters

As a full-length story progresses, the character will be forced to make difficult decisions and do things they would rather not do. They will be in a position where their desire will be tested and to overcome they will have to find the ability to persevere. If it was easy, it wouldn't be a big deal to them and shouldn't be the subject of a full-length story. If it's just a matter of watching a character for two hours as they walk to the store and get their ice cream, there isn't much to be learned about a character. What should have been a two-minute walk that turns into two hours and much hardship to get the ice cream, that might be a full-length story.

These are just some guidelines as to what a long story should aim for. This is in an attempt to use the qualities that a full-length work has to the best effect. When people watch a movie or read a book they'd like to be moved. If all you give is slice of life episodic situations, they might like it but they likely won't be fully satisfied.