I go back to things my dad said: "Your career is long and the business world is small. Always act with integrity. Never take the last dollar off the table."****
About 15 years ago, I saw an Oprah show where she said, "Always be the only person who can sign your checks." At the time, I had no money. I was at Second City in Chicago. I came to New York in 1997 to work on Saturday Night Live. I realized I have no head for business. And it would have been very easy for me to let someone take control of my money - for me to say, "Here, sign my checks...whatever."
Finally, grad school also gives most folks a healthy dose of intellectual humility. That was certainly the case for me, and that's not a bad thing either.
I can't remember who told me this, but I certainly didn't grow up knowing it, so I must have gotten this advice at Salomon Brothers in the 1970s. The advice was, first, always ask for the order, and second, when the customer says yes, stop talking.