Why Is Estimation So Hard?

I live in Cambridge, UK; my family lives in Bristol. Software timescale estimation is like estimating how long it will take me to visit them. Given a strong tailwind and no traffic, I can tell you how long the drive takes. But if there is road work or a traffic jam, if my car breaks down, I leave late, or I travel at rush hour, then this estimate becomes a lot less reliable. Foreseeing some of these problems, I will commit to a likely arrival window. I know the best-case journey time; I have an idea of the worst case (I've had some nightmare trips). I can judge an expected arrival time somewhere between the two. However, I can't ever fully account for the unforeseen—if my car breaks down, I'm stuck. Mobile phones are ...

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