weakest link in the chain

is it just me being arrogant or is it true that sometimes the client is the weakest link in the chain? How many times have we presented design work that is bang on, or an advertising campaign that is edgy and delivers on the brief, only to have it rejected and then 6 months later realise we were right?

Perhaps the most delicate, nuanced, and difficult part of the design process is gaining buy-in. Anyone have any thoughts on how to achieve this?