The first bite is with the eye
I think I first heard the phrase “the first bite is with the eye” from a TV chef, but it applies equally to the software creation process as it does to cookery.
A user’s interaction with a piece of software or web site is as much emotional as it is functional. Compare the soft, warm, fuzzy feeling you get when first interacting with a product from 37 Signals, say, to the stomach churning reaction you get when booting up Lotus Notes, for example.
This immediate emotional response will pervade the whole of a user’s long-term impression of a product, imbuing their relationship with whatever feeling was conjured up in those preliminary interactions. They say that in most job interviews the interviewer makes up their mind within the first 5 minutes. The same is equally true for software.