There's nothing wrong with being someone who smiles at a stranger. There is a strength in kindness, and in happiness. Being happy or kind, is not weak or naive. I always tell my kids, if you're smiling - then people can't help but to smile back at you. It's almost instinctive, infectious even. It's as if smiling is a reflex that we're born with, rather than a learned behaviour.
In some ways, isn't that the truth?
We have to actually work at being unhappy or dissatisfied. It's so much easier to smile and make light of things rather than to hang on to the things that make us less than happy. Who wants to hang onto all of that heaviness? That, is work and effort - and almost counterintuitive, never mind counterproductive.
Life gets in the way of our own personal happiness sometimes. It's easy to get jaded and bored; it's easier to be grumpy and go the path of least resistance....give in to being that mouse on a wheel circling mindlessly, endlessly....with no real endstate to speak of. What's there to be happy or excited about when it's the same thing day in and day out....or you feel like nothing is exactly the way you thought it might be.
That's why it's always important to rise above. It's always important to smile - even when you don't feel like it. It's not just for the outward appearance you give to others; but most importantly for youself. Sometimes, if you keep on smiling - you just won't have to work at it so much anymore and then suddenly....you're just happy.