There are no (very few?) universal rules in tech. The HN advice to buy instead of build is correct in the majority of cases where a startup isn't actually doing

There are no (very few?) universal rules in tech. The HN advice to buy instead of build is correct in the majority of cases where a startup isn't actually doing anything revolutionary on the tech side (and there's nothing wrong with that! Bringing proven tech to an industry that doesn't have it is a great business model). It sounds like Jane Street does not fit that model.