Of course, this only made sense when Apple was more of an underdog to IBM, and Ciro Santilli greatly admires their defiance of the norm.
As of 2020 however, Apple is kind of on the top of the mobile world, and Think different simply makes no sense anymore, notably because it relies on closed source offline software used by millions.
This is a trap every company that prides itself on it's "alternative culture" sets for itself. If they succeed, they could become the norm.
Figure 2. 1976 Think different. 2011 Think mainstream. Cropped from wallpapersafari.com/w/RqYUEj.
Video 1. 1984 Macintosh advertisement by Apple (1984) Source. This ad suggests that Apple was the new thinker that would destroy IBM, as Steve Jobs said it himself when introducing the ad: www.youtube.com/watch?v=zlQvMp5rB6g. And then Apple became IBM in the 2000's starting with the launch of the iPod and then leading up to the iPhone.
Because the people who are crazy enough to think they can change the world are the ones who do.
Video 1. Source.