Introducing PEAR, the functional SOLID

    This guarantees that your software isn't going to crash
    because of an unhandled exception, and allows you to think
    in different ways.

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.

See also most every time someone thinks, "I won't raise here, I'll just return nil".