Can you imagine St. Augustine having trouble with his Latin? He did.
"Now here I used the word "cupi:" will you tell me whether it should be "cupi" or "cupiri?" And I am glad this has come in the way, for I wish you to instruct me in the inflexion of this verb "cupio," since, when I compare similar verbs with it, my uncertainty as to the proper inflexion increases. For "cupio" is like "fugio," "sapio," "jacio," "capio;" but whether the infinitive mood is "fugiri" or "fugi," "sapiri" or "sapi," I do not know. I might regard "jaci" and "capi" as parallel instances answering my question as to the others, were I not afraid lest some grammarian should "catch" and "throw" me like a ball in sport wherever he pleased, by reminding me that the form of the supines "jactum" and "captum" is different from that found in the other verbs "fugitum," "cupitum" and "sapitum." As to these three words, moreover, I am likewise ignorant whether the penultimate is to be pronounced long and with circumflex accent, or without accent and short." (Letters of St. Augustin, Letter III, to Nebridius, AD. 387)