There is nothing like the adrenalin rush of a fast-growing startup. And depending on where you are in your life/career, it can be a huge boost even if it ultimately fails. The growth period is one in which you can take as much responsibility as you can handle; usually are not rigidly fixed to one job description. It’s as close to a meritocracy as possible (ignoring Silicon Valley sexism and ageism of course). If you can live with uncertainty and change, there is nothing like it.