Anecdotal, but I recently wrote a book that had a quote from a prominent, successful person at the opening of each chapter. Part of my process was reaching out to the originators of these quotes and asking permission to include them.

The result was fascinating. With exactly one exception (from a university professor) all the people I was able to contact were incredibly gracious and encouraging. Based on that experience I now believe that to have significant success really does require a reflexive attitude of generosity and gratitude. I don't think successful people are paragons by any means, but when I compare how they responded to how the average person would respond to a stranger asking a favour, I have to say - I'd definitely trust a random billionaire over a random member of my own social class.

I used to work for many extremely wealthy individuals when I was at a firm, and I wouldn't trust any of my clients farther than I could throw them.

I would absolutely trust a random homeless drug addict over the random self-made billionaire. You don't acquire a billion dollars by playing nice, fair, or by the rules, and the norm is for them to treat people as exploitable resources. Being nice is the exception, and generally something only done when it provides some sort of benefit to them to further their exploitative capabilities.

I don't know that it's really indicative of grace if you phone someone and ask "hey, I'm including quotes from prominent, successful people in a book, do you mind if I add you to it?" and they say yes. You haven't really asked them for a favour, really you're doing them a favour by improving their reputation.

yes, but 'best of luck with the project', or 'sorry I don't have time to read an advance copy' goes beyond what's expected with that kind of power differential. I do think most average people would have felt much more entitled to someone admiring their thoughts.