What would be a good one for open source? It should be a key to success. What is the one thing you need (other than a lot of money) to make it in the open source world?
That's it. Don't pretend to be something you are not. Don't pretend to be a fan of open source when you're not. Don't pretend to be "supporting open source" when you're not. Don't pretend to have features you don't have. Don't pretend to put resources against something you don't plan to invest in. Don't pretend you will meet an arbitrary deadline.
The reason this commandment is so vital is due to the way open source market battles are played out. Your cards are always on the table, face-up. In the proprietary world, you can play FUD games, you can pretend to have features that are still in development. This just doesn't work in open source.
The same goes for financial shenanigans, legal shenanigans, PR and marketing shenanigans. The next half-naked lady I see in an open source booth will be the first.
It's all pretty transparent here, and I think that is a very good thing indeed. Unless, that is, you can find an example of opacity that worked.