I was a bit hasty of the entropy of the passphrase, my mistake. I still stand by that even if we choose from 2048 common words, generating a good passphrase (one that isn't a common sentence) is harder than we think.
Here, I just generated you a few passwords:
* hefty march attempt force bowel scuff
* between sepia book sweat lemma saint
* safe warn magical cask hefty wish
* alum glib puck adieu dour lazy
* telephone pine cavort good knee swank
* numeral plan jewel conch slate tube
* pastry piano sure proxy unit brew
* trig rise taint current sans gallop
Here is the same random numbers but encoded into ascii instead of words:
* 81Pk3t?Rq6S}
* ]CPcYrT^?iE3
* +qV`J9ZU&.,C
* `>sp=~V);3g>
* E&_ff7a|Z4B[
* ?OX~[J>0K'S*
These each have the exact same amount of entropy as the word-based ones.
I just watched a friend using some kind of long password and it took about a minute to get the password correctly entered. Easy to look at the keyboard also when he was typing and guess the words used.
Here's Merriam-Websters 3000 _core_ words [1]. Here's a list of 355k words [2].
That someone has selected 2048 words used to generate passphrases, doesn't make it easy to remember.
Everybody uses more than a few thousand words on at least one language. And selecting the least used ones will make your passprhases easier to memorize, because they have much more concrete meaning (by virtue of their rarity) than the most used words.
http://www.economist.com/blogs/johnson/2013/05/vocabulary-si...
The words don't have to be incredibly simple, either. Grabbing a random GfyCat image from the front page gives me "OrangeLankyBasilisk" which is easy to remember, none of those words are particularly foreign. But they're not in your list of most common words, nor are any of them in XKCD's simplewriter [1], which keeps track of the 1000 most common words.
[0] https://github.com/a-type/adjective-adjective-animal/tree/ma...
[1] https://xkcd.com/simplewriter/
Edit: The words need to be randomly chosen by a computer, so it doesn't matter what the most common words are. You could generate the password from a list of 2048 spanish words or japanese words or emojis and the entropy is the same as the previous scenario (assuming the attacker knows your dictionary of symbols just like they'd know your dictionary of English words). If you let a human choose, of course the smiley-face and poop emojis are going to be picked 50% of the time, but that's not the intention of the comic or passphrases.
If the human is picking anything than there WILL be a bias in selection. Effort should be made at minimizing that, but even with education this is a difficult task for any worker.
It got to the point where I actually took a classic literary work and made a 'password words' dictionary from it just so that I could have the computer generate possible new passwords. (there bias is mostly filtering out things that might be offensive... because someone can always take it the wrong way even if you explain in advance the theory of how the password was created by a computer).