Buffer Overflow Causes. ©2002, Jedidiah R. Crandall, Susan L. Gerhart, Jan G. Hogle.  http://sfsecurity.pr.erau.edu
All sorts of other far-fetched but deadly-serious things you should think about.
User input is not always what causes buffer overflows, they may be caused through things like environment variables or race conditions. 

You don’t have to know all about environment variables or race conditions but if you’re managing a software project then your programmers should.