If you are a realist you will just seem like any old regular pessimist to an optimist.
When approached by an optimist with an idea that seems impossible to work for countless reasons, your first instinct as the realist you are will be to help them but pointing these out.
However, these “helpful” objections that you bring up will be like nails on a chaulk board to the optimist who is looking for support and supplementary ideas, not objections.
In improvisation acting, there is a key phrase that helps actors to continue creating the scene in realtime for the audience.
The key phrase is “yes, and…”
When a co-actor makes a comment, they respond by starting a sentence with “yes, and…” in order to think of something that will add to the scene that they are playing out.
If you are a realist, you can use this to deal with optimists.
Your realism will be very useful to the optimist once they have expanded the new idea that they have had. They will need someone to bring them down to earth and help them to figure out the problems with their idea so that they can make it better.
But that is not step one.
Step one is to expand the idea by providing additional ideas.
Don’t reply with “no, but…”
Even though you might be thinking about all of the stupid ways their idea will fail, try “yes, and…” instead. The time for realism will come later.