One of the greatest offenses in the world of writing is to have a sentence that doesn’t quite make it. Something is missing, like the rest of your thought.
Your sentence gets going really well and then…it suddenly isn’t there. Perhaps you got sidetracked or put a period where a comma belonged. Your computer automatically thought you were starting a new sentence, so the first word that should have followed the comma is now facing a period and is capitalized. Don’t blame your computer. Instead, blame yourself for not proofreading the document.
If you are an undergraduate, take heart. You have company. They are called graduate students. Yes, even in graduate school, fragments can be a part of an essay. They shouldn’t be, mind you, but they are.
If this is your problem, the thing to do is to proofread everything. Read it out loud, if you please. Have a friend look over your writing, if you are so sick and tired of that paper than you simply can’t look at it again.
Fragments are not good things, unless you are doing creative writing. Even then, a few fragments go a long way.