Seven years ago, Airwallex co-founder Jack Zhang walked away from what looked like the deal of a lifetime. Stripe Inc. was offering to buy his firm for $1.2 billion and legendary Sequoia investor Michael Moritz was urging him to accept.After weeks hashing out the details and sale price with Stripe’s billionaire co-founder Patrick Collison, Zhang was close to agreeing. Then doubts crept in. He called a vote with his three co-founders and over a WhatsApp call they decided to turn the offer down....