There are several reasons why estimates may be inaccurate:
1. Lack of Information: Incomplete or incorrect data can lead to flawed estimations. 2. Optimism Bias: Overestimating positive outcomes and underestimating potential challenges. 3. Complexity: High complexity in projects makes it difficult to accurately predict outcomes. 4. Human Error: Mistakes made by the individuals responsible for the estimates. 5. Changes in Scope: Unexpected changes in project requirements can render initial estimates invalid.