"I don't know" is useful until it isn't.

If we're heading into a disoriented future, the first thing we're going to say is: "I don't know." And that's okay. Professionally, I've tried to never leave it at just "I don't know." I always say, "I don't know yet." Because it's okay not to know; if you're a consultant or a professional, eventually, you need to know. "I don't know" is a temporary state, not a permanent excuse.