A missed bus can cost more to the person with no flexible hour afterward.

The same twenty minutes is not the same twenty minutes for everyone. Someone with a shift starting at nine and a supervisor counting lateness loses pay, standing, perhaps the job, while someone whose morning can absorb a delay loses only a coffee. Reliability in transport is not a convenience question, it is a question of who can afford the failures.

If you set schedules or judge lateness, ask what the journey actually required of the person in front of you. And if your own morning has slack in it, be careful about assuming that everyone else’s does too.