Some of us can want something so badly that we seduce ourselves into believing that we can easily obtain it with little effort. We simply don't see the pitfalls or the preparation necessary to accomplish our goal.
Then we wonder why we fail time after time or get blindsided by the unexpected. We have a warped perception of the task ahead of us and ill prepared to accomplish it.
We need to learn pessimism is not always a negative viewpoint but a necessary check and balance needed to formulate a plan of action. Anticipation of events and situations that could derail our plan allows us to see early enough to respond by modifying our actions in time to minimize or circumvent the problem.
Flexibility can only happens if we are prepared to modify how we are accomplishing the task while maintaining the goal. Progress is always incremental and may require detours to arrive at our final destination.
Optimism provides the fuel to get started while pessimism keeps us prepared to respond to events.