This seems obvious. Your frame of mind when you first see a photo, or any piece of Art, affects what you will see and what you will take away from it.
While this is obvious, I think we forget it. Try posting a photo for critique in several different online venues, with different cultures. The wild variability of responses reflects (of course) the differing tastes of the venues but also the differing cultures.
In many venues critique is approached essentially as a 'find what is wrong with the picture' task. Others fall more directly into 'how much does this picture resemble the ambient taste' and a few, occasionally, reach for 'what is good about this picture'.
The point is, though, that your frame of mind has a large effect on how of look at a picture. If you know it's a Great Photo you look at it one way, if someone's just showing you their snaps you look at it another, and if someone's asking you to help them take better pictures, you'll look at it yet another way.
Witness the occasional games that are played by people posting well known photos "for critique". This first of all illustrates the deep ignorance of many would-be critics, but also illustrates the different mindsets we use when we approach a picture. If you approach "Migrant Mother" with a mindset of 'what is wrong with this picture' you'll find a lot, and profit very little from the experience.
Ideally, you should approach a picture with a clear and open mind. Look neither for greatness nor for flaws, look for what is.
You'll get more value from it, be it a throwaway snap of drunk girls, or a Victorian masterpiece of portraiture.