Peterson's 12 Rules For Life, have you heard of this?

[Rev. Rye]

There's the lefts fundamental inability, right there.  Incapable of firmly grasping any high ground they actually possess, squandering it in the process. 

And in my experience, the left tends to possess a lot of high ground (far more than the right, anyway), and the more radical leftists work under the assumption that the moral high ground is all they really need, and manage to squander it while they prove their point.