Bhagavad Gita, Chapter 17, Verse 24

Therefore, uttering 'Om,' are the acts of sacrifice, gift and austerity as enjoined in the ordinances, always begun by the followers of the Vedas.

This real practice, beginning with one specific sound, is named here as a longstanding, deliberate tradition.

Krishna ties this opening syllable directly to Vedic injunction, not personal preference. Real consistency across generations is what gives this practice its weight.