Here is the dictionary definition: an optimist is one who usually expects a favourable outcome. While this does not seem like much, words are essential.
- There is no obligation to always expects a favorable outcome
- Favourable is a very ambiguous term: favourable for you? others?, the earth's ecosystem?, the universe.
This definition is quite helpful because, as often, it is very nuanced. This is fully compatible with the pursuit of happiness: you can sometimes be pessimistic about any given outcome (no stress!). Usually, with wisdom (and an examined life), you can redefine favourably as you see fit.
The most efficient lifelong lessons come with a direct and very real immediate negative outcome. For instance: a car accident, sports injury, significant failure, or losing a loved one. Optimists will consider all aspects of this event and redefine the situation (or the story) to find a positive outcome.
Being optimistic is a choice. An optimist in action looks for a reframing of any adverse situations. This can happen immediately, but more often than not this requires a heavy dose of introspection and soul searching.
As stated by @theStoicEmperor:
Personal challenge and key takeaway: Today, please try to look at at least a negative situation and look for a positive outcome.