sentences:  The correct decision regarding whether to switch is sometimes obvious, particularly when there is the largest difference in advantage.However, borderline and counter-intuitive cases are relatively common, and switching strategy is hard to summarize.While an often-quoted rule of thumb is to choose the option that forms or preserves the best single hand, this is unreliable; sometimes it is even correct to break up a natural by switching, for instance in the case AT + T[3-8] "vs." dealer 7, 8 or 9.