[jhchabran]

It's a quite common problem, I faced it myself some years ago. Basically, changing your target without any achievement like you did means you're avoiding to complete your task by starting a new one.

You may flag this as procrastination or not, but you're asking us here how you could stop changing targets while you should ask yourself why don't you want to complete your tasks ?

Usually, when you start something and guess how much work learning something require, you underestimate it.

When you're halfway in, you got a more precise estimation. That's where you may get bored, faced to the great amount of work required to complete it.