It's in the type/amount/quantity of food, exercise(or lack thereof), concurrent medications, stress, caffeine, other illnesses, hormones, age of the insulin, absorption of the infusion set, temperature outside, body temperature,alcohol consumption, and a thousand other little factors. Sometimes, there appears to be no earthly reason for it.
You can graph carbs.
You can graph boluses/basals.
You can graph exercise.
But how can you graph a morning in which you consume 3 caffeine-laden beverages,(exact caffeine amount "unknown") run around like nuts, clock in a 205 at lunch(stress or caffeine?) bolus for that plus lunch, promptly get low 1.5 hours later and again 3.5 hours later, go high and the infusion set promptly falls out..
I'd give up, but that's apparently not allowed. Neither is sledge-hammering one's meter or shaving one's head/joining the Peace Corps.
It's still tempting, though.