The human brain can only handle so many different items in a given category - it seems to be limited to seven. That's why there are seven days to the week, seven digits in telephone numbers, and seven Dwarves. Brands in product categories also follow the Seven Dwarves Rule - there are usually about seven products competing in each category, and each one usually has owns unique attribute that differentiates it from the others. It's not that products don't share attributes in reality. It's just that in the customers' perception, the proximity of competing options transforms what may be minor differences into defining differences.

Without research, you can't know your product like your customers do. You know the inside details - what it takes to build it, all its components, and all the configuration possibilities or flavors or bundling options. But what your customer knows is usually only one thing (or one brand attribute) based on a single need; it's the fast one, or the complete one, or the best one for kids, or the one that's easy to assemble. When it comes to owning category space in the customer's brain, brands usually get only one chance for a label, and it's up to you to make sure it's the right label.