Who but Himself could trouble Him? Christ was troubled, because it pleased Him to be troubled; He hungered because it pleased Him to hunger. It was in His own power to be affected in this or that way, or not. The Word took up soul and flesh, and whole man, and fitted it to Himself in unity of person. And thus according to the nod and will of that higher nature in Him, in which the sovereign power resides, He becomes weak and troubled.
St. Augustine, quoted by St. Thomas Aquinas: Catena Aurea.