>Picking the proper names for software constructs is also part of that category. I'm always impressed at how choosing a slightly wrong-one can have a huge impact down the line.

Similarly I'm often shocked at just how critical name disambiguation is. There's a shocking number of extremely similar concepts when writing code which, when given the same name ends up causing bugs.

A good example is 'file' which can be used to refer to a file handle, file name, file object of some other kind, a 'file' representing an aggregate of information on person, and often it ends up referring to directories, devices and links as well.