When your working on your own track your brain sort of hears what it wants, compensates, etc. over time and your picking out the individual elements not the whole sound.

Before you EQ you should listen to other stuff or have some peace and quiet for a bit then do your EQing for no more than an hour or so before taking a break and coming back to it.

Also you can get used to your monitors/speakers and these may "colour" the way you mix your final production - it's always nice to have a second set, even if they're just crappy hi-fi speakers, so you can compare the sound on both sets.