First of all djb is https://en.wikipedia.org/wiki/Daniel_J._Bernstein and the accomplishment was releasing a secure email server (qmail), a secure webserver (publicfile), and a secure BIND server (djbdns). Both qmail and djbdns became widely used, and the main alternatives were projects supported by large teams.

It took 8 years before the first bug was found in these projects.

I highly recommend reading through the guidelines in https://cr.yp.to/qmail/guarantee.html for how to write secure software. In particular point 5, Don't Parse, is broadly applicable and under appreciated. A well-known class of bugs arising from this error are SQL injection attacks.