Every person grows up thinking they are unique and special. Your mother told you that and, to this day, you believe it. The customers coming to your web site are no different. They each come expecting you to deliver an experience that is custom-tailored to their exact needs and desires. They want you to remember them, what they did, what they like/dislike and what they will likely do in the immediate future. Meet these demands and your product (website, et al) is the shit! Meet it not (sorry for the pseudo-Braveheart riff) and your site is shite (which is the opposite of “the shit!”).
There is no possible way you could deliver each of your customers a generic experience that would meet their expectations – they believe. But they’re wrong. With enough traffic through your application, patterns emerge. These patterns become evident through regular, vigilant review and analysis of your usage analytics (aka “the data”). Very quickly you start to see which users are performing specific actions and the correlations between those users. Add in a healthy dose of user profiling and you start to fill out your “typical” customers. Augment your findings with some qualitative research (yep, talk to your customers) to understand their motivations and very quickly you’ve moved away from individual snowflakes into similar “piles” snow – also known as personas.