We need to unload stuffs from our mind

I am currently reading a book called Getting Things Done by David Allen. I learned from there that our mind will remind things that we need to do, usually when we can't do something about them. In other word, our mind doesn't know when is the right time to remind us. That is why when we think of something, usually I think that it should be done now. This distracts me from what I currently do and most of the time results in nothing done. 

Another thing that I often experience is that when I set reminders, somehow I do not feel like doing it. This may indicate that I am not fully clear on what those tasks mean to me. The intended outcome is not clear that perfectionism may also come and cause fear as the standard is high and unclear.