Bhagavad Gita, Chapter 2, Verse 41

Here, O descendant of Kuru, there is but a single one-pointed determination. The purposes of the undecided are innumerable and many-branching.

A focused mind moves in one direction. A scattered one pulls itself in a dozen at once.

The intellect is what actually steers a person, more than the mind itself. Trained toward one clear aim, it holds steady. Left undisciplined, it keeps splitting off in new directions and never settles anywhere.