On more than one occasion I've been working on some code and can't quite figure out what's wrong and had another set of eyes take a look and they find the issue in minutes. This continues to convince me of the value of a pair programming model where two people collaborate more quickly rather than waiting hours/days to find and correct an issue. I think that once you get fixated on a problem you can begin to make it more difficult than it really is. Another set of eyes will look more at the code more objectively and likely notice something trivial that you have filtered out because of seeing it for so long. Finding the correct balance of two working together at intervals and independently otherwise can be difficult but two heads are probably always better than one particularly when you are in a hurry to get a system out.