Those are unique per year, so the phrase "a simple but potentially" is counted many times. There are about 600 million google 4-grams, slightly more than there

Those are unique per year, so the phrase "a simple but potentially" is counted many times. There are about 600 million google 4-grams, slightly more than there are 4-character ascii strings. Summing up, a meaningful 4-word phrase, is, in the terminology of the article, "risky". My advice: use generated passwords, and apps like 1password to remember them.