[hug]

Commiserating together means validating each other's negative feelings about something.

You may commiserate with a team member when you both get made redundant, as a healthy example.

When a team of several engineers are all thrown under a bus by a PM, they may commiserate with each other about the workload they find themselves with, as a slightly less healthy (but common) example.

But when you, as a manager, commiserate with the team about the PM throwing you under the bus, you are doing your team and the organisation a disservice, in that you're creating an unhealthy us/them dynamic when doing so, and the other things the article suggests.