Over the last 3 years, I've read and listen to everything about productivity

But all of it can be boiled down to one useful question, asked every day:

"What's holding me back right now"

To find out why this question will dramatically increase your productivity, read this:

First we need to understand what constraints and non-constraints are.

Imagine a chain. Regardless of how strong all the other links are, the chain can only carry as much as the weakest link.

The weakest link is the constraint holding back the chain.