If there is one thing that will stand the test of time, it's thumb placement on mobile devices. This makes consideration of the "thumb zone", a term coined in Steven Hoober's research, an important factor in the design and development of mobile interfaces.
Have you ever interacted with a mobile website or app that simply didn't play nice with your thumbs? Perhaps you've had to stretch to get to an important menu, or swiping turned into a battle with multiple swiping elements. Mishaps such as these reveal poor consideration of the thumb zone.