The phrase applies to negative results not positive ones because the rest of the phrase is it's not the people it's the system which implies a problem not a good result. Going through all the details of the system is more than I'm willing to type. If you'd like to know more these are a few of my favorite resources.

Multipliers by Liz Wiseman

Beyond Command and Control by John Seddon

First Break All the Rules by Marcus Buckingham

The Effective Manager by Mark Horstman

Dare to Lead by Brene Brown

The Effective Executive by Peter F. Drucker

You're Not Listening by Kate Murphy

Four Thousand Weeks by Oliver Burkeman