Because you aren't your customer. And what you said isn't true, although most engineers I know believe it. It's not A/B testing or bust, and design isn't seri

Because you aren't your customer. And what you said isn't true, although most engineers I know believe it. It's not A/B testing or bust, and design isn't series of arbitrary aesthetic decisions. You can also gather (non-numerical) data by going out and talking to potential customers, figuring out exactly what they need, and then making design decisions with that as an input.