Culture is a direct reflection of leadership. This is one of the reasons ego-centric leadership - fear, greed, self-importance - is so incredibly self-defeating in any organization, but especially in startups. It's the main reason my own companies went on to do OK, but not great. I was scared - that we'd fail completely, that the opportunity cost was too high, that we should secure the small win rather than risk it all again and again.
It took me about a decade to truly understand that leadership is about people, not things. What a platitude, but what truth! The abstractions take care of themselves if you just take care of the people. I came late to this realization, later perhaps than necessary given loving parents and a decent education. I think this is just one of those growth journeys that we're all on (seeing my daughter develop ego is very gratifying, though I know she'll have to get over it eventually!). For some this realization comes sooner, for some later. Don't let reductionist materialism fool you: leadership is first and foremost about people, not things.
Equally, beware of falling into the converse trap: the ego is only a hindrance to success if it is inwardly focused. If the flow radiates outward - to the thing you're looking to do and the people you're doing it with - you're unstoppable. You will be called magnetic, charismatic, inspiring. Even if you have all the social awareness of an Erlich Bachman.
Perhaps this is why large companies are less successful over time. The manager's primary motivation is personal success and the "I" will get in the way of truly caring about employees, customers, colleagues, and making good products.
The point in time when you've reached product/market fit and sit back and say "now we have to become a real company" is one of the most dangerous, pivotal moments in a startup's life. It's where culture gets lost, empty mission statements are formulated, useless lists of values circulated and dominator hierachies installed. Rules and processes can't substitute for creative, purposeful founder leadership.
You can only show up as that purposeful leader day in and day out if that's who you authentically are. And that authenticity is one of the things I increasingly look for when investing.