Bhagavad Gita, Chapter 2, Verse 61

The steadfast, having mastered them all, sit focused on Me as the Supreme. His wisdom is steady whose senses are under control.

Discipline alone isn't the goal. Discipline pointed toward something worth focusing on is.

Restraint on its own is only half the equation here. What actually stabilizes the mind isn't just holding the senses back, it's giving them somewhere real to focus instead.