It's a relationship that can be very complementary. The 8 is attracted by the calm, the stability, the tenderness, the generosity, the tolerance and the discretion of the 9. The 9 is attracted by the energy, self-confidence, leadership and intensity of the 8. The unpretentious presence and affection of the 9 soothes the 8. Also, the 8 likes to have control and to make decisions, which is often all fine for the 9. The 9 tend to live through their partner by merging with them, so the intensity of the 8 allows the 9 to feel alive. They are both sensual, with big hearts, and like to have a safe and quiet haven for both.
The 8 can see the 9 as being too passive, indirect, indecisive, ineffective and oppositional. The 9 can see the 8 as being too demanding, domineering, intimidating, confrontational, excessive and uncompromising. When the 9 feels under pressure, he does not respond, becomes evasive and adopts a passive-aggressive attitude. This can make the 8 even more furious. And the 9 becomes even more iced and resistant. Also, the 8 may neglect 9's opinion when he thinks he is right, which can frustrate 9 if he feels ignored.