A Real Programmer keeps his code locked up in a card file, because it implies that its owner cannot leave his important programs unguarded.
--Real Programmer's Don't Use Pascal
Why do programmers reinvent wheels? There are many reasons, reaching all the way from the narrowly technical to the psychology of programmers and the economics of the software production system. The damage from the endemic waste of programming time reaches all these levels as well.
--The Art of UNIX Programming
As innumerably many programming books report (I myself have no idea where I first read it), experienced programmers tend to carry with them a sizable selection of utility code they've built up over the years -- those general-use routines which just missed inclusion in the standard libraries but don't justify an external library by themselves. I too am guilty of a hubristic, eponymous extension to the C language -- libdank.