Never upset your star-point stones
The direction of play from a star-point (hoshi) stone is towards the middles of the adjacent sides. Allowing the opponent to play at those points makes your star point sad.
The meaning of this proverb is that, relative to other opening moves, the value of a hoshi stone is extremely contingent on how you develop it. What Kajiwara is trying to say is that if you choose hoshi in the opening, you should make the utmost strategic effort to get those critical points.
The position from the book that inspired this proverb is this:
When Black approaches with , White makes a two space high pincer at . Black foolishly plays , sparking the joseki to . Black's marked hoshi really wanted to have a friend around . Letting White play there instead by choosing this joseki, Black makes his star-point upset. Poor star-point. :-(
According to Kajiwara, the correct direction of play would be to play the approach at immediately, without -. If White then enclosed the lower right by playing at , then Black could take the mutually big point at (or a) and his star point would smile.