Keep it small and simple (KISS)
The KISS principle is one of the most important principles in software design.
A program which becomes overly complex will not only also become unmaintainable, but a security risk as well, since complexity is the enemy of security. Additionally do complex programs need more resources and tend to become bloatware.
The Unix paradigm to “do one thing and do it well” is directly connected to the KISS principle
See also How we measure