[font color=\'#000000\']I agree with AWeil, mood has a lot to do with it. I always think my best work comes when I am relaxed, and "eyes wide" on the world.
For me, it's the difference between looking (actively seeking out) and seeing (passively allowing yourself to observe) -- I do best when I am "seeing". It's funny -- I can feel myself slip into this zone, and once I do, it's often hard to stop (a problem if your driving home...!)
When I went to Yosemite for the first time, the weight of all the great work that has been done there was heavy on me: how can I add to this, or find my own voice? But as I walked around the trails, it surprised me how much more beautiful the park was than anyone has ever captured. So there was still work to be done there! And luckily, Ansel (et al) already captured all the primary images, so I didn't have to waste my time recreating them. I could sit back and enjoy the sun setting on Half Dome, and look for my photos elsewhere.
So the challenge for me is to try to remember that there is always something new to be found, whether visiting a master's old stomping grounds, or simply shooting another still life of a flower.[/font]