My team might be half decent. So might the dozens of other teams working on the code base over years and years. Everyone will certainly have the best of intentions. But mistakes will certainly be made. Misunderstandings will occur.

Note I said "now let's scale" -- it's pretty easy to rely on good practices and a steady hand when it's a dozen engineers in a room. When it's a thousand engineers in three timezones it's a fair bit harder.

Edit: typo