An aphorism is not an argument; it is too well-bred for that.
Thus Susan Sontag.
Here’s the quote in context, which makes it more clear but less true:
Aphorism is aristocratic thinking: this is all the aristocrat is willing to tell you; he thinks you should get it fast, without spelling out all the details. Aphoristic thinking constructs thinking as an obstacle race: the reader is expected to get it fast and move on. An aphorism is not an argument; it is too well-bred for that.