I have been wanting to talk about this for some time. I often find that when I am putting a track together the levels of concentration can be really intense, so much so that you find yourself telling yourself "I will have to give this a rest for a while". The amazing thing is that I probably notice more about the track when I am NOT concentrating so intensely. Literally playing the track and getting on with something else within ear shot, even sideways on often makes me notice something. The human brain is amazing at how much information it can pick up when you are not directly looking at or hearing something, you just have to trust it.