Well, you could be forgiven to think that if you wrote i=5; some code and then i=12; that 'some code' is executing with i set to 5. Instead all code is run with i=12 because there is only one value for a variable per scope.

This can lead to extremely annoying bugs because your brain is wired to read and understand this stuff sequentially rather than all at once. I've stared at some page of OpenSCAD code for a long time before realizing that it was yet another one of those footguns.