I don't know how you do it.

Telling someone you "don't know how [they] do it" is sort of a compliment.

Sort of. 

But it's also a backhanded way of announcing, "You're doing it the hard way!" or, "I'm glad I'm not you."

It's the opposite of empathy. It's a public declaration that you don't really want to try to imagine another person's situation.

Personally, "I don't know how you do it" is one of those compliments that I'd like to never hear again.  In full disclosure, I will also admit that I've most certainly used this compliment before. I've probably used it right here on this very blog.

For this, I apologize.

I'm going to do my best to never let it pass my lips again.

Updated to add: I mean, it's not just the words that are bad - it's the sentiment behind it that I could improve upon, right?