Language works against us in identifying subjectivity. Too often we reflexively reach for a description formulated with the copula. This reifies our subjectivity into an assumed objectivity but does so in an epistemologically duplicitous way. It's a very old trick, and it still works on us. The cogito functions the same way.
To paraphrase the head DEA agent in The Limey: "There's one thing I don't understand. The thing I don't understand is every word you just wrote."