I think there is also a small-but-real random effect.
And there is also your opponent's actions. On very busy routes(Hong-Kong - Singapour), with pleny of flights, every day is different, with a different planning, different planes going into B, C or D check, etc..... so you really cannot stabilize.
I had made some tests by setting different prices for each day. Worked somewhat, but the limited increase in revenue was not worth the hassle. IRL, companies certainly do that, though.