"Ego has nothing to do with the capitalization of the pronoun I. Printing and handwriting have everything to do with it. In Middle English the first person was ich--with a lower-case i. When this was shortened to i, manuscript writers and printers found it often got lost or attached to a neighboring word. So the reason for the capital I is simply to avoid confusion and error. Of course, some writers refuse to be bound by this convention. Two of our favorites, the poet e.e. cummings and Don Marquis, author of archy and mehitabel, both favored the lower-case i" (Morris Dictionary of Word and Phrase Origins 303).

In Middle English, the first person singular was expressed with "ich", eventually shortened to "i" in the lower case. But printers encountered difficulties setting the lower case "i". The letter would be dropped unintentionally or run together with the words that followed or preceded it. So the original purpose of capitalizing the "I" was to make it stand out from other single letters and provide it with the status as a whole word...

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