This talk from Adam Mosseri about being data informed is great. It is worth the thirty minutes. At 13:00 in he says the line that makes this post's title. He then shows two examples from Facebook where the data sent them in wrong directions. These are my summaries of the reasons:
- Most of your data is generated by your power users, so if you aim for increasing pure engagement you will market to this group only.
- When you optimize for one piece of data you will eventually ignore anything that is not measured by the data.
I think that both of these points contain great truths for teaching.
Bonus quote, "The greatest risk is taking no risk at all." (29:20)
UPDATE: Forgot the link.