Pessimism means wishing you’d do things that will make your future better. Optimism means wishing you’d do things to make your present better.
If one thinks there is little future left, that they may die soon, or if the reality of death is top of mind, then they will look back and wish they had done more with their life. Travelled more. Met more people. Had deeper connections. Had more experiences.
If one thinks they have more time left, that death is inevitable but not in the equation yet, then they will look back and wish they had done more of the things that make their present and future better. Pushed themselves harder. Taken more responsibility. Faced bigger challenges.