It is a term and strategy that Luke Wroblewski coined which in a nutshell is about using the mobile web as a constraint to think about desktop web design and development decisions.
Now, when I say re-think your mobile first strategy I’m not saying that the above ‘mobile first’ is wrong. In contrast, what I’m actually saying is that your thinking/interpretation of ‘mobile first’ is wrong (and of course by ‘your’ I mean those other people that are doing it wrong, not you).
Many times when people begin to talk about utilizing this strategy, they start with picking a smartphone, and in most cases that’s an iPhone. However the problem with that is it actually causes you to isolate the ‘normal’ web from the ‘mobile’ web. Thus forcing a interpretation of ‘mobile’ as being on a iPhone like device, when in fact to different people this means an array of varying things. To some it may mean their smartphone, a tablet, their super manila-envelope thin laptop or their whole setup that they bring to Starbucks. By defining it your way, it tends to force the belief of false user context stereotypes and inevitably yields an incomplete experience for users.
Creating context stereotypes for mobile users such as they’re always in a hurry, on a slow connection and are only interested in a super quick interaction encourages you to develop websites to target those users. However, the fact is that most likely — if you haven’t tested your own users, they’re probably using their devices while watching TV. If these are indeed your users, this means they aren’t in a rush, and they’re most likely on a strong WiFi connection. Below are a set of principals that many people tend to create based on false context stereotypes:
Mobile First is about developing a better user experience, so you shouldn’t be trying to define what your definition of ‘mobile’ is on your users. Instead you should be willing and ready to adapt. To make it easier, you should instead probably be thinking of an Experience First strategy, so that this would help you to focus on the actual experience — regardless of the platform.