If you survey 100 students just as they're coming out of the exam hall, 99 of them will say "I could have done better had I studied harder".
Ever wonder why?
I think it's human nature to procrastinate. It's quite natural for many of us to keep postponing the inevitable. If the deadline is not imminent, we slow down. As the deadline comes closer, we speed up.
Therefore, it's very important to have a deadline for every day. Then you might stop saying "Only if I had worked a little harder..."