What is the best piece of advice a complete stranger ever gave you?

[BigDog_Fan]

Some of the most useful advice people carry around for years did not come from a parent, teacher or close friend at all, but from a genuinely random encounter with a stranger, someone met once on a train, in a queue, at a bar, or during a difficult moment, who happened to say exactly the right thing at exactly the right time without any real stake in the outcome themselves. There is something about advice from someone with no ongoing relationship to protect that can occasionally land with a directness that people closer to us sometimes struggle to manage.

It does not have to be anything profound or life changing on paper, sometimes it is a single offhand comment that just happened to arrive at the right moment in someone's life. What is the best piece of advice a complete stranger ever gave you, and do you think it would have landed the same way coming from someone you actually knew well?