"Definition" has a lot to do with the amount of detail the viewer thinks is there, or should be there. So while I agree most people will inevitably put their noses up against a giant print after viewing it at a normal distance in order to see how much detail there is, I've seen people do that and become wowed by a lack of detail too. In some ways that can be an even more fascinating experience because it is somewhat baffling for a viewer to see the work at a distance, then walk up to it and find there isn't nearly as much detail as he thought there was when he was standing back. To some extent the mind compensates and extrapolates or "fills in" detail. Even with small prints, if the subject matter is highly detailed this visual phenomenon can trick people into seeing high sharpness and minute detail in a grainy print that actually might be fairly low in resolution. If you inspected very small areas of the print one at a time you'd see mostly fuzz, but when viewed as a whole image from a more reasonable distance one tends to see implied detail in addition to what is actually in the print.