Technically, it just tries to save energy: new things tend to take more brain time, because the brain has to learn how to do them. That's why it tries to "trick" you into not doing that important thing. And instead of getting ready to your next exam or tomorrow's meeting at work, you go read some interesting article on a blog or watch again an episode of your beloved series, surf the facebook or instagram (or, another blog on how to fight procrastination :) ).
As a result, in the beginning you feel yourself better - because you do what you like, not what you have to - but that's just for a short time. After some time, your brain (the same brain that made you procrastinate, remember?) now "whispers" into you the feeling of guilt, makes you unhappy you didn't do what you have to, that you're lazy. Now you end up with a not finished task and with a movie (blog post) that doesn't make you happy.
That sounds bad, but here are the good news - there's a way to make yourself into doing that important (but "unpleasant") task. And the trick is - simply start doing it.
It turns out (some scientists found out, if you want to learn more, you can search for it) shortly after starting doing the work, you forget about that fear and reluctance and do what's needed much better. You get a working mood and have a better concentration on the work, too. You get into the process. After some time of doing your work, you forget that feeling of fear and discomfort and work normally. So, the only thing left is to just start doing it.
One of the ways that may help you get into that working mood is by dividing your work time into periods, interleaving them with breaks. The length of a period is rather personal, I try to change it time to time, some times using 21 minute work periods, some times 44. You work for 21 minutes, than have short break, than again.
This is what this page about:
The post seems a bit cumbersome and not complete, but you have to forgive me - I'm neither professional psychologist nor professional personal trainer. Procrastination is one of my main problems, probably, thus I started writing the app - first of all to help myself do better and do more. If you google on the topic, you can find a lot of information and tools. I learned something from a course on Coursera called "Learning how to learn": https://www.coursera.org/learn/learning-how-to-learn. It is a great help to anyone who wants to improve his learning, working skills. And it is free and easy to follow, take it - won't regret.