Robert C. Townsend's 'Up The Organization' is a classic business book from the sixties.  Checking it out on Amazon, I came to the conclusion that it's as good for you today as it's always been. Townsend was the CEO at Avis who appointed DDB and approved the famous 'We try harder campaign'. Here's how he tells the story:

You have to love that 6-point philosophy. As an agency person, it's hugely inspiring and motivating. Damn right that would get you the agency's best people and best work! On the other hand, to some clients, I imagine it could seem downright irresponsible. (Though note that Avis did still retain the right to reject DDB's proposals, just not to amend them.)

According to an Avis website:

During those first meetings between DDB and Avis, a
simple question was asked by DDB, “Why does anybody ever rent a car from
you?” The reply is what made advertising history: 
“We try harder because we have to.” DDB’s top art director, Helmut
Krone, already intended to center the campaign on the phrase:
“Avis is only No. 2.”
It was copywriter Paula Green who remembered what she learned
during those first research meetings with Avis, and added the now-famous
phrase: “We try harder".

In an attempt to convince potential customers that Avis
simply tried harder than everybody else, the entire ad campaign was
focused on frank and truthful statements about Avis’ business
philosophy. To communicate this to the field, the entire management team
at Avis traveled to every branch location across the country, spoke with
every single employee and explained that the success of the campaign and
of their business hinged upon providing superior customer service every
chance they got. Each Avis employee also received a copy of new Avis ads
in his or her pay envelope before each campaign would run. In just one year, the campaign literally changed the
fortunes of the Company.  Prior to the campaign, Avis had just $34
million in revenue and losses of $3.2 million. One year later, revenues
had jumped to $38 million and for the first time in thirteen years, Avis
turned a profit of $1.2 million. The biggest short-term success of the campaign was found
in Avis’ market share, which grew from 11 percent in 1962 to an amazing
35 percent in 1966.

And the ads themselves still look surprising and challenging today. No logo.  No pictures of cars.

But my god, they worked! Reminds me once again that you can't do amazing work without the trust and support of an amazing client. (Luckily, we have some.)