Some Ruby evangelists claim that strong typing is unnecessary in the presence of unit testing. I disagree with this, and here's an analogy:

Using a dynamically typed language is like being drunk at a party and having to ask for everyone's name over and over again. When you are using a strongly typed language everyone has a nametag. And is sober.

It's not good enough that something is possible, it has to use as little of my time, energy and brainpower as possible.

Here's another analogy:

Programming in a dynamically typed language is like learning kung fu then going blind.