The fundamental activity of software development is _learning_. Although it looks to an outsider like the main thing is typing stuff in (or pasting it in :-),

The fundamental activity of software development is _learning_. Although it looks to an outsider like the main thing is typing stuff in (or pasting it in :-), the thing that takes all the time is learning what you should type, or learning why the code you already typed in isn't doing what you expected. If you've done that exact project before then sure, you can estimate how long it will take to do it again. But that isn't often the case - usually we're trying to do something new, or better, or on a different platform. Always learning.