My interpretation is that having an explanation for something is useless if you can't actually make it happen. And even if you don't fully understand how something works, it's good to be able to use it.

For example, I would much rather be able to use a computer than know how it works.

Also, if you can't do it, that calls into question whether your explanation is actually valid. Anyone can explain something, so long as they're not required to actually make the explanation useful.