Requirements volatility is the core problem of software engineering
It's now been more than 50 years since the first IFIP Conference on Software Engineering, and in that time there have been many different software engineering methodologies, processes, and models proposed to help software developers achieve that predictable and cost-effective process. But 50 years later, we still seem to see the same kinds of problems we always have: late delivery, unsatisfactory results, and complete project failures.