I'll never forget the feedback I received on a paper from one of my professors:
"Beautifully written as always, John, but lacking in substance."
She was correct, of course – I hadn't started reading the source material for my essay until the night before the paper itself was due.
With so little time to reflect on the material, I didn't have much to say. Sometimes last minute panic can spur you to heroic action in a short amount of time. But there's no shortcut to letting your ideas marinate.
When you give yourself time to set your work aside and return to it later, you can examine it with a fresh mind.
Only then can you craft something of true substance.