I had to test posting this here directly from Quora . . . because it’s there (here) and I could . . . and it worked!
OK, so I’m not a Software Engineer. Heck, I’m not even an Engineer, but I did sleep in a Holiday Inn a few times; plus, I worked with Rocket Scientist, Engineers, and Mechanics for over two decades, so I know a little bit about the animal. I also worked in Project Management, including some software development and IT architecture efforts.
This is a really good – and entertaining – analogy of the problem posed in the question. Make sure you read the comments as well, because there are some add-ons that extend the analogy to include other issues not raised directly by the author of the answer. There are 80 answers to the question, but read the top one; the one that got well over 3500 votes. Read the others as well if you want to. Far be it from me to tell you what to do. While you’re at it, if you haven’t been to or heard of Quora before, you might want to check it out.
Engineering Management: Why are software development task estimations regularly off by a factor of 2-3? 80 answers on Quora
Why are software development task estimations regularly off by a factor of 2-3?
Photo shamelessly stolen from Professor Tomasz Zastawniak