Work estimates must account for friction
If your project estimates include eight hours of work per employee day, you're gonna have a bad time.
Karl Wiegers
Karl Wiegers is the author of Software Development Pearls, from which this article is adapted. He’s the Principal Consultant at Process Impact and the author of numerous books on software development, project management, design, and other topics.
Plan for tradeoffs: You can’t optimize all software quality attributes
An essential part of requirements analysis is understanding which quality characteristics are the most important so that designers can address them appropriately.