The effectiveness of the PayPal network stems, in part, from the fact that it includes all the elements needed to put together a start-up: Talented engineers and entrepreneurs with innovative ideas and a love of the start-up life; experienced managers who can turn ideas into businesses; and financiers, most notably Mr. Thiel and Mr. Botha, but also Mr. Hoffman, Mr. Levchin and others, who have used their PayPal money to become angel investors. The fact that most key PayPal employees were in their 20’s and 30’s, and not ready for retirement, helped too.

The long hours, sleepless nights and intense pressure of life inside a start-up often create strong bonds among its employees. In its early years, PayPal was all about pressure and the struggle for survival. The company was losing millions each month. It was besieged by hackers who used technological trickery to siphon off huge sums from the company’s coffers. And it faced blistering competition from, among others, eBay, which eventually admitted defeat when it shut down its own online payment service and bought PayPal.

Mr. Levchin said the pace at PayPal was so intense that employees had little time for much else. “We all became each other’s social life,” he said. “Because of that, we formed really deep connections.”

Many of those bonds were already in place, and life at PayPal merely strengthened them. From the beginning, PayPal hired people whom its founders or other early employees already knew.

Mr. Thiel tapped his network of friends from Stanford, many of whom had worked at the Stanford Review, a libertarian magazine that Mr. Thiel co-founded in 1987. They populated PayPal’s business ranks. Mr. Levchin, for his part, hired engineers in large part from his alma mater, the University of Illinois at Urbana-Champaign, which had earlier been home to the team that developed the software that would be the basis for Netscape’s Web browser.

One of the first engineers Mr. Levchin hired at PayPal, for example, was Russel Simmons, who went on to become a co-founder of Yelp. Mr. Simmons, in turn, helped convince another engineer, Yu Pan, to join PayPal. Mr. Pan went on to become one of the first people hired at YouTube. Other University of Illinois recruits included Mr. Chen and Mr. Karim, two-thirds of YouTube’s founding troika. “YouTube is like a PayPal reunion,” Mr. Levchin said. A YouTube spokeswoman declined to make Mr. Hurley and Mr. Chen available for this story.

The long-standing bonds created an atmosphere of openness and trust, which not only helped PayPal succeed, but also made it easier for members of the network to embrace each other’s post-PayPal projects.