About certain things and not others. On some days. How we see our world depends in large part on the condition of the filter we use: How much sleep we got last night, what we recently ate, how were we raised, and what we think life is really about etc. I think this is the primary goal of all thos eastern philosophies like Buddhism and Hinduism.
I don't think continual contenement is part of the human condition. We thrive with a changeable outlook, challeneges big and small to keep our minds active, occasional sadnesses to make us appreciate being happy - contentment on a continuous level is just not good for us.
Call me materialistic but with a lot of money I could be content. As the saying goes, life is like a sh*t sandwich. The more bread you've got the easier it tastes.
Sometimes I am truly content. Most of the time I am not. When I am not, I am forced to look at what is causing me to not be content, and generally after I've done the work, I am more content than before.
So I think that yes, it is possible to be truly content - for periods. And that it is impossible to avoid times when we aren't content. And that those times are what force us to grow.
One point of view is that it is human nature to want things you don't have (or to want to do things you haven't done). If you don't achieve these then you will be frustrated. But if you do, then either the achievement doesn't meet up with your expectations and you are again frustrated or else it provides only momentary satisfaction which soon disappears and is replaced by another, different, desire. Either way true contentment is impossible.