A virtuous circle might look something like this.
Key attributes are relevance to the task / issue at hand; timeliness; accessibility and usability. Did the client get what they needed, when they needed it, how they wanted it, easily?
Similarly, a vicious circle might look a bit like this -
The wrong thing, the wrong way, at the wrong time.
Key is that you're always building up or running down trust - so if you consistently go round the virtuous circle, you'll probably be forgive one bad interaction, and your client will pay attention whenever you appear on their horizon. But if you consistently go round the vicious circle you are likely to be ignored - even when you start offering a virtuous circuit. Share of mind achieved is not transactional, but based on previous experience.
Where does this apply? Pretty much all customer and client interactions - plus a lot of on-line interactions. Think about community members, blog-readers, tweet followers, etc.
And, of course, sorry if I've just wasted your time.