[edmundsauto]

But for results to generalize or to understand why, the confounders must be accounted for in the randomization. This is really hard to do well -- there are often subtle influences that aren't sufficiently understood how they impact these non-linear systems. What makes someone convert? A million different factors; changing the color of a button in one context doesn't necessarily tell me much about how people would respond to that experience in another context.

It's easy to underestimate how complex things are, because we only see some superficial aspects of e.g. a user/software interaction model. This flaw is down to how our brains work -- ref "What you see is all there is".