Benedick means that, first, he and Beatrice know one another too well to overlook each other's faults and thus "woo peaceably". Second, he means that they aren't naive like some people and because of this, they realize that people have faults. In Act 2, sc. 1, first Benedick (ll. 236-237), then Beatrice (ll. 273-275) indicate that they have had a previous relationship that turned out badly. This former relationship gives them knowledge of one another that lovers in a new relationship don't have. People in new relationships tend to only see the good points because they are starry-eyed with the wonder and excitement of a new romance. Claudio and Hero are examples of this. Those two are filled with a hot fire in their romance. But hot fires burn out quickly oftentimes, whereas a slow burning fire, such as Beatrice and Benedick have, will last a long time. Several times there are references made to the wit possessed by both Beatrice and Benedick (Act 1, sc. 1., ll. 61-62 and ll.142-143).