Comment by antrod

One other thing to consider about the big market hypothesis is: how accessible is it to a capital efficient startup. To take an extreme, the power generation market in the US is second only to health care, but it is quite unlikely that you can crack that as an entrepreneur. Similarly, even if you can get into a big market, the amount of margins available to subscale players is often a deterrent in and of itself (you can't for instance become a subscale ISP these days even though Internet access is a huge market as well). Outside of chasing a fad, going after inaccessible markets is the second biggest mistake I see.