When it comes time for basking in the glory of a campaign's success, it can be tempting to want to take the lion's share of praise for yourself. After all, you – the account manager and primary face of the agency – have been the one working most closely with your client. You have sweated blood (and possibly cried a few tears) to make the campaign a success, and your client knows it. However, for the sake of your conscience and the goodwill of your colleagues, it's far better to give credit where credit's due and share the limelight.
The very nature of an agency means that no one part of the team can work in isolation and be totally effective. The three core components (account management, creative and strategy) are symbiotic and rely on each other to build a mutually-beneficial team and produce great results for clients. For any one person, or one part of the agency to take all the credit would be unfair, and selfish.
It is also imperative that your client believes that the whole agency is indispensable, not just one person (e.g. you). The agency/client relationship has to weather the storms of key people leaving (e.g. you), or being moved onto other accounts (e.g. you).
The irony is that the inverse to this principle is quite different. If something goes wrong, then it's usually one person who has to wear the blame (e.g. you), rather than the whole agency. Account leadership demands accountability, and the buck for accountability stops right at your feet. If you strive to be considered a respected account manager you will be content to both shoulder the accountability and share the credit where it's due.