Why are decisions hard?

From the book Making Hard Decisions, there are four sources of difficulty:

1. A decision can be hard because of its complexity.
2. A decision can be difficult because of the inherent uncertainty in the situation.
3. A decision-maker may be interested in working toward multiple objectives, but progress in one direction may impede progress in others.
4. A problem may be difficult if different perspectives lead to different conclusions. Or, even from a single perspective, slight changes in certain inputs may lead to different choices.