Procrastination my friend....
An evil power, that enslaves thousands of people every year, causing them to fail their exams.
The only way to beat it is to START. Once to take the biggest step and start revising, you'll find it hard to break the cycle. At the moment because you aren't revising. Its easy to say ill do it tomorrow.
Once you start, its a whole lot easier to keep doing it
Its like going to the gym. Everyone says they want to do it, but they never do. But once you go that first time. You'll make a habit of it