This is important in more than just startups and software/websites. This is important is pretty much everything. Designing for human factors should be incorpora

This is important in more than just startups and software/websites. This is important is pretty much everything. Designing for human factors should be incorporated as early as possible in pretty much everything, from software, to physical user interfaces (with actual toggles and such), to boring old registration procedures (done with paper!). If you accept the premise that you should be designing for human factors at some point, then you should be applying it as early as possible to save you the most money, time, and generate the largest return. Your minimal viable product should have undergone some sort of "design" when it leaves the door. It doesn't have to implement everything, or even most of it. It just has to be ready to grow into something that does.