When I "am on", I look at every possible move for my opponent. The problem is, it is not natural to "be on", especially when what we see in front of us, looks obviously good. Sometimes, when I find what I think to be a crushing move, I don't even look at every possible move that I can make. Then again, we are human ;-)
I think it comes down to discipline of thought.
Just wondering but often time when I play I make a move out of impulse not much thinking and often blunder anyway the important thing is when u play do think from your opponent side of the board? or just the few important ones.