Erasion of question and focus

I wanted to share an experience i encounter from time to time. Namely, when pondering on some topics, it sometimes feels like i found something important and in the same moment i begin to focus on this topic, it begins to slide away. First, the answer that seemed to be almost developed, fades. Secondly, as i try to re-formulate the question, everything that question is based on, also fades. On the screen of imagionation it is always like some kind of massive movement - like flowing lava or sliding landscapes etc.

After that, i am basically left without memory of what seemed to be in very close reach. How should one approach to such experience? Is it something common and explainable or is it some kind of personal fantasy?

Edit: One should not post the question on the first impulse, sorry for the inconvenience.

One more edit: basically i think this question is quite valid, but i doubted my motives when asking (laziness?). And since the focus must be on the work we do ourselves, it would not benefit me, if somebody answers the questions i can and must find answers myself.