Someone might write, for example, “There are too many sos in this sentence,” in response to:

So many people were present, so he said so, so they were all so very pleased, but others felt that attendance was not so great, was, in a word, so-so.

But “sos” is hard to read. It looks at first like a mistake. Using italics might help a bit but not much: sos. Another option would be to add an apostrophe: so’s. But MLA style uses apostrophes only to form plurals of letters: p’s and q’s.

Note that dos and don’ts is fairly well established—that is, in the dictionary—but dos by itself seems as uncomfortable as sos. (In the thought balloon above the reader’s head might appear, with multiple question marks, “disk operating system” or “save our ship.”)

Consider sidestepping, rewording, when the imperfection of language rules causes this kind of trouble:

The word so appears way too often in this sentence.