It's been said that "a strong backbone is the key to surviving in the world of PR$."$ What does this phrase mean?

Public relations involves a lot of metaphorical "heavy lifting," such as climbing the corporate ladder to become an account executive.

Rejection$-$by potential clients, by journalists pitched a news release, by the public$-$is a daily occurrence in the world of public relations.

Competition for accounts from colleagues inside a firm is the primary reason PR professionals cite for leaving the industry.

There is no $"$l$"$ in "team"; when many hands are put to a task, a high tide lifts all boats, and a strong backbone makes the dream work for this teamwork.