Perhaps a better way of phrasing your question would be:

How do you handle the "mental component"
of a ride when you are attempting an event that is harder
than anything you've accomplished before?

My own tactic is to avoid thinking about the enormity of the task at hand. I never think about how long, how difficult, or how painful a ride "might become" just for the sake of worry. I always focus my "mental" view on the immediate conditions I'm experiencing, and what is needed to reach a "meaningful" fraction of the overall event.

Keeping my focus on incremental goals, such as an "hour by hour" inventory of my performance, or split times for 25-mile segments, or making a certain town or fuel stop at a certain time are all ways of occupying the "mental needs" of a ride.

Marathon runners seldom think about an entire race, even while they are racing. They focus on their pace -mile by mile. And only think about the entire distance as a means of maintaining their goal focus.

Hope you get your 200k. Good luck.