One other thing he touched on in passing: people are assuming they'd know what to build from the start. Even in relatively trivial applications a lot of work goes into finding the right way to express what you're trying to build. I recently worked on a small app and spent 40 hours trying out different approaches to the user interface. The solution I went with could be coded up in about 2 hours, but I had to do 38 hours of work that eventually got thrown away before I arrived at it.

This sort of thing happens all the time in professional software development. Sometimes it is a waste of time, e.g. people rewriting things in a new language/framework for negligible benefits, but a lot of it is a necessary part of developing a polished app.