You should probably know that they're out there, since it might be dangerous if you happened upon them unexpectedly.

There's no set way to encourage a meeting - most happen unexpectedly and spontaneously.

An error may also be an exception, which is something that happens unexpectedly.

Correspondingly there may be output demands created by control operations which result in things happening too quickly or unexpectedly.

But usually it happens unexpectedly, as though the person has pulled a knife on me.

A miracle is something that happens unexpectedly at the moment it is needed.

But if he draws good things, a bad thing will unexpectedly happen.

Children repeat behaviors that happen unexpectedly because of their reflexes.

Those crises do not suddenly happen unexpectedly, as with natural catastrophes.

Something may happen unexpectedly where you could make use of it.