House of Cards
Being a software developer, it's easy to recognize the importance of having a great environment to work in. Most of the time I spend tends to be 80% or more on thought and the rest of the time translating those thoughts into actual code. I have politely explained this process by making the analogy of building a house of cards.
When you're working on software (and other thought-provoking tasks) you invest time to work toward a point where you have to translate your thoughts or "purge" them into code or words. If you are interrupted during that crucial phase where you're building your house of cards, there's a good chance that part or all of your house will fall down. At that point you can sometimes quickly pick up where you left off if only a few cards were lost. Other times you have to file a complete loss with the "house of cards" insurance adjuster and rebuild from the foundation up.