MacKenzie Scott says her college roommate loaned her $1,000 so she wouldn’t have to drop out—and is now inspiring her to give away billions

MacKenzie Scott has been one of the most generous philanthropists during the past few years, and an episode in college may help explain why. 

After finalizing her divorce from Amazon founder Jeff Bezos in 2019, Scott ended up with a load of shares she earned from helping to build the e-commerce giant during its early days, when she helped with business plans and contracts. Upon their divorce, Scott received roughly a 4% stake in Amazon, or about 139 million shares at the time. 

Since 2020...