Here is a good example video of what I am alluding to: https://www.youtube.com/watch?v=9CgOthUUdw4
Maybe I should refine my blog post or include the video in the explanation?
What I found was most people over/under estimate things. They also tend to do it consistently at the same rate. Typically they have a scaling factor you can use. Around 3 seems to be the sweet spot for most people. You could just as easily use 3.1 or 3.2 and get a similar answer. I usually go for 3 because I can do that in my head without a calculator.