Charles Ellicott Commentary Psalms 78:8

"And might not be as their fathers, A stubborn and rebellious generation, A generation that set not their heart aright, And whose spirit was not stedfast with God." — Psalms 78:8 (ASV)

Stubborn. — Refractory.

That set not their heart aright. —Literally, did not establish their heart, which preserves the parallelism better.