Yes and no - you can not test it all, there might be a point of diminishing returns after a certain level of optimization that has gone into a site. Just as wit

Yes and no - you can not test it all, there might be a point of diminishing returns after a certain level of optimization that has gone into a site. Just as with SEO - SEO is not completely useless, yet there are people who promise too much or even hurt you. I suspect with A/B tests you could also hurt yourself, for example if you measure the wrong thing. I don't know, maybe I am just a little bit tired of all the simplified promises.