A psychological barrier to code reuse in a commercial setting, NIH ("Not Invented Here") Syndrome is attributed to the supposed individuality of software developers. They would rather do work themselves than rely on the efforts of others.

There is some truth in this. But programmers don't like useless, repetitive work any more than anyone else. Take the parser generator combination Lex-Yacc. These are used extensively by people creating parsers for simple command lines or scripting languages.

So when is NIH syndrome ever an issue? Something that might look like it to an outside observer is when programmers express trepidation over using a module that they're not familiar with because they have concerns over how effective it is. As with Lex-Yacc, when a module or tool that the programmer knows he can trust exists, he is likely to use it.

A lot of programmers enjoy what they do. Creating something yourself is more enjoyable than using something Not Invented Here. If programmers lose sight of the project deadlines and start enjoying themselves (heaven forbid), NIH syndrome can easily set in.