There's this idea being successful means being on your A-Game all day, every day. Never wasting a waking-moment, and most definitely never taking any down or personal time. Our society is work-oriented. That's just a fact, and not necessarily a bad one. It simply means we don't place value on taking a moment in the hustle and bustle of every day to stop, sit, and breathe.
I think it is completely unrealistic to expect yourself (or anyone else, for that matter) to be able to keep a smile on your face at all times. In recent years I've noticed that there is this notion that being a "positive" person somehow entails never having negative feeling of thought about anyone or anything at any time. No--if you're one of these "positive people," there is no room for unhappiness, sadness, or upset; positivity must be all encompassing at every time of day...doesn't it?
Positivity relates to your outlook on life as a whole. Each day brings its own challenges, heights, and depths, and it is unrealistic (not to mention unhealthy) to trap yourself into a rigid shell of a person who is only allowed to feel one side of the spectrum that is emotion. That isn't positive. That is constrictive. Damaging. Inauthentic. And it surely should not be what is the societal "norm" when a portrait of an individual who has a positive outlook is conjured up.
Brainstorm an image of a "positive person," and who is it that comes to mind? Is it a co-worker who is always wearing an ear-to-ear smile? Is it the friend that sends cheesy and slightly overdone inspirational quotes to you every morning? Is it an aloof and unbothered acquaintance? Everyone shows emotion in different ways, which is something that in American culture we are not taught nor do we as a whole make an effort to understand. We value hard work and conformity; we place importance on shutting up and pushing your problems to the side. Because everyone knows that that's healthy. But, if you can do this, and do it well, you will be thought of as successful. Do it with a smile, and you're a beacon of positivity.
I think resilience is one of the biggest tellers of a positive outlook. Despite what pitfalls are thrown, or what past demons may be knocking on the door at night, a person who can still find the passion, drive, and reason to see the beauty of life is a better example of self-generated positive mindset. People who feel the depths of their feelings, yet don't allow themselves to be sucked into the trap of wallowing and pity--those are the people who are truly inspirational.