Almost a decade ago, Google, Apple, and a slew of other tech companies had a "gentlemen's agreement" not to hire each other's employees, or "poach" employees, as it was otherwise known.
Yet, in 2005, Google allegedly tried to contact a few of Apple's Safari engineers to work on their Chrome project, and this pissed off Steve Jobs to no end. Jobs called Google co-founder Sergey Brin to say that it was going to be "war" if they hire any one of those people. Now, those employees really were valuable: sometimes it could take months to get someone up to speed with the tasks (and secrets) a former employee might have had. Jobs famously had a short fuse, and he wasn't going to back down to another big name tech leader when it came to keeping people he saw valuable.