You want to do something, to achieve a goal, to start a new activity, whatever. You make a plan about you should do for your change. On the first everything goes smoothly, but then the next days, you don't have that much ambition and you feel like you want to give up.
Well, as much as I hate to say it: you're your own enemy. You're fighting between the part that says "come on, get up, do that now" and the part that says "why should you change anything?you'll feel better if you don't do anything". You seriously need to do something about the second part.
Changes are good, but you need to be receptive to the idea that in the beginning is going to be hard to make that change become a habit. What you need is a specific plan among some things that you should remember. First of all, when you want let's say to start tomorrow learning at biology(for example), well you prepare your pen, pencil, you set your alarm clock at the desired hour, you take an empty notebook and you prepare your books. You don't just say "I'll learn starting tomorrow" because that's vague and as you know already: you won't do anything. You'll just watch movies or play games, whatever you're doing in your free time. Secondly, you have to remember that the beginning isn't easy, you need to fight the you that doesn't want to get out of his comfort zone. Think about the final result. Think that if you want to get there you need to put a little effort in what you're doing now.
The war with yourself doesn't begin and doesn't stop here. It's another problem when you're feeling depressed. That slows you down in everything you do, no matter if you want to have fun or to read a book. Don't be too hard on yourself if you're not feeling well. Everyone has there ups and downs. The big difference is between the ones who want to do something about it and the ones who don't. Listen to a song. Call a friend that makes funny jokes and makes you feel better. Do something you like until you feel better. Don't say it's impossible, because if you want it, everything good can be possible.
The biggest enemy in your life is you, and maybe you're sick of hearing this, but accepting this truth is the key to understand how can the good part in you win. Knowing yourself is the best weapon. And don't forget that your attitude counts, so if you want to live at your full potential accept change and don't think low on yourself because that will only slow you down.
I know I haven't been discussing this until now, but it seemed a good subject, as it covers many problems with ourselves. Reaching perfection is a foolish thought, but reaching what you really want is the perfect reality.
