What is the most important ingredient to success in PR - the client perhaps?

I am not sure if the title's assertion is obvious or not or if anyone agrees.

The most likely answer would be who you pick as your PR including DIY PRs.

However, I have come round to the fact that the clients' enthusiasm, interest in their communications, how they rate PR in terms of priority, relationship with PR agency and what they have to say are at least half the equation, if not more. You would expect the PR to be enthusiastic and reasonably knowledgeable as given, wouldn't you?

On the other side of the coin people are busy and PR is often an extra thing to occupy their time.

So how to square things? It is as much about the agency picking the client as it is about the client picking the agency.