<p><pre><code> This guarantees that your software isn't going to crash
because of an unhandled exception, and allows you to think
in different ways.
</code></pre>
OTOH, it also means that if you mess up in one spot - for instance, passing an array of things you thought were numbers but were actually characters to `sum` - you don't get any indication there's a problem until later when the result is used.<p>See also most every time someone thinks, "I won't raise here, I'll just return nil".