Pessimists and Optimists both can see and understand the conclusion, the goal, or the end result. Both can apprehend its value and importance. Both can even desire it. What makes one a pessimist vs. an optimists is now how one perceives the end, but the space between the self and the end.
Optimists see the stepping stones to achieving the goal.
Pessimists see the barriers and road blocks that keep them from the goal.
Realists believe both are viable options and operate in the world, neither on the promise of hope, nor on the defeat of despair, but rather on the power of volition, the captivation of willpower to achieve accomplishments.