I first heard this mantra at Google, which was far from a startup even when I joined in 2006. It could easily afford to try and find the right fit for people. In fact it took the opposite approach: you were only allowed to move around and try a new job or position if you already were doing well in your existing position. Internal transfers were seen as a reward for good behaviour, or perhaps it was to avoid bad employees avoiding detection by constantly moving around between managers.