Wise Old Indian Saying

In the James Clear email this week a Michel de Montaigne is quoted as saying, “The most certain sign of wisdom is cheerfulness.”
When I look up the meaning of wisdom I am drawn to that. Wikipedia says “Wisdom is the ability to apply knowledge, experience, and good judgment to navigate life’s complexities.
I like that it says it is the “ability to apply knowledge…”  The reason I like that is the way I see it.  Knowledge tells me there are many problems.  Every night I watch the news and hear about problems of violence, climate change, cost of living and now a polio outbreak in Papua.  Those all represent the tip of the ice burg. 
I do not hold to the view that wisdom is evidenced in the wringing of hands over problems or the angry statements that something has to be done my way.  The application of a solution is in my mind a considered thing, that while acknowledging a problem, enjoys life while living out a solution.
I am unsure if that makes sense, but the existence of problems does not mean I have to be miserable.  If wisdom is the application of knowledge rather than just knowledge, then I am responsible for my part.
With climate change for example I can only pick up after myself and leave the world at the very least the same as I found it.  Merril and I often make a point of leaving a place we stay better than we found it.  That may not solve the problems of the world, but it does solve a  problem in our part of the world.
Collective wisdom is to me everyone doing what is right.  That is, knowing the problem and applying the solution.  To me it is best if I do it  because I want to not because I have to.  When something is forced on another it generally engenders resentment.  The best ones to tell others of the benefits of something are those who have freely chosen to and experienced the benefits of something.
Why I think cheerfulness comes into the equation is that wisdom to me is not the singular domain of the guru with eyes half closed speaking in monotone or of the one wringing their hands and bemoaning problems.  It is the realm often of common sense.  The experience of the everyday person.  The one who sees a problem, applies a solution as best they can and moves on. 
After all, problems are a part of life and not the whole of life.