Complexity increases the possibility of failure; a
twin-engine airplane has twice as many engine problems as a single-engine
airplane.
By analogy, in both software and electronics, the rule
that simplicity increases robustness. It is correspondingly argued that
the right way to build reliable systems is to put all your eggs in one
basket, after making sure that you've built a really
good basket. See also
KISS Principle,
elegant.