The fifth point in the HBR article is listen, even (no, especially) to the weird ideas. This point is a little harder for me to understand because I have never been a big fan of the weird or unusual. I have always liked the "play by the book" type of thinking. This has lead to me judging other ideas too quickly because they are "weird" or the ideas are coming from "weird" people. That seems to be what HBR was meaning - if I'm not humble enough to learn from anyone then I am limiting what I am able to do.
Many times the "weird" ideas come from highly curious people who can easily get off course. Even if some of the ideas are not worth considering, I can't let myself then assume all the ideas are not worth listening to just because of the source.
At the heart of humility is the realization that I don't have all the answers and that others are needed to find the best solution. Sometimes the "weird" ideas are the best ones to hear.