Yes, code can "suddenly" develop bugs, if something external changes, such as the environment or input data (remember Y2K?). Just because "it's been working for years" doesn't mean it can't break in the future, even without a code change.
Re^6: Keeping, and advancing in, your job
Replies are listed 'Best First'.
Many of those applications that were hit by Y2K were developed 20+ years earlier and were supposed to live for 5-10 years. They were way out of spec.
It's arguable that 2-digit years were a premature optimization, hence a bug.
The point behind me statement is that many younger developers feel that code "rots" - that it will break in spontaneous ways if they don't get to rewrite it. If it worked yesterday and, all things being equal, no-one touched the code/environment, it will most likely work today.
Being right, does not endow the right to be rude; politeness costs nothing. Being unknowing, is not the same as being stupid. Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence. Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.