How to keep motivation when doing anything

 Whenever you feel very strong motivation at first when doing something, but by the time, your motivation is gone away?

Don't worry! That's normal. Everyone got the same issue with you. Let have an example. If it's the first time you learn to play piano. You are total new without any knowledge. A few first lessons, you learn musical notes, you know buttons that are represented for each note. You feel excited since you discovered new things, and it's simple and easy for you. You are enthusiastic waiting to the next lesson. But by the time, more complex and difficult technic come to you. You struggle with them. It takes you more time. And you start feeling less motivation. And finally you quit, thinking that you don't have ability to play piano.

That's because you don't know practicing V session. (Mindset secrets for winning by Mark Minervini)

The V session start with a relatively easy task, moves on to difficult part, then end with another easy task for strong finish. This takes advantage of the serial-position effect, which is a person’s tendency to recall the first and last events more vividly than the ones in the middle.