The distinction, and this is why offices are important to me, is that in a coffee shop you can 99% expect that nobody is going to come up to you and bother you.

In an open plan, that expectation is nearly 0%. Even if you're wearing headphones and wrap yourself in custom made police tape labelled GO AWAY, someone will still come up to your field of vision and poke you in the shoulder.

A friend of mine has a sign on the back of his chair that say something like "Please do not disturb me when I'm wearing headphones." and people still disturb him because it is easier than emailing him.

His manager told him that he's "unapproachable". LOL!

My favorite interruption: "Just wanted to check if you got my latest email"

3 minutes after they sent it.