Put one crab in a bucket and it climbs out. Put several in and none of them ever will, because each one drags down whatever gets above it while hauling itself up. Jinson uses that to explain why the people around you may not want you to succeed, and he offers two reasons: they never managed it themselves, and your managing it would make them feel worse.
His post on selling is the other good one, and it argues against the received idea. Being told you have the gift of the gab is not a compliment about selling, because customers do not want somebody who enjoys hearing himself. He points at the old line about two ears and one mouth and means it as an instruction rather than a proverb.
The training posts are more promotional and get built around a quiz that sorts you into a category before the answer arrives.
Read the crab post if the people closest to you have been quietly discouraging and you have never been able to name why.