How does the culture of an organization influence the quality of estimates?

Project management

1. Why are accurate estimates critical to effective project management?
2. How does the culture of an organization influence the quality of
estimates?
3. What are the differences between bottom-up and top-down estimating
approaches? Under what conditions would you prefer one over the
other?
4. What are the major types of costs? Which costs are controllable by
the project manager?
5. Why is it difficult to estimate mega project (e.g., airport, stadium)
costs and benefits?
6. Define a white elephant in project management. Provide a real-life
example.