The other variable of course, particularly for a digital image, is the ambient light. I sometimes find that an image that I have PP'd in the evening looks less well in the daylight of the following morning. I have said this before I know but one of the best pieces of advice I was given came from the head of the photographic faculty of my local Technical College (fellow club member). He advised (in the days of mainly prints) "
stick it on the mantelpiece and live with it for a few days" and then see how you feel about it. I've always found that to be good advice and it raises two questions in my mind. Given that your mentor must have quite a few other photographers on his books, how long is he able to study your image for. To what extent was he judging your work against a common norm when you might have been trying to create/recreate a particular mood. I will admit to preferring the second but I was more than happy with the first. Perhaps sometimes it's worth applying the maxim I quote to my other half on occasion. Once you have bought what you want, stop looking in shop windows. You might just see something you like better when it's too late.
P.S.that was a bit of a rant.