Imagine everyone has giant rubber hands. Know also that they all forgot their monocles & will use your app while running down a flight of steps at full speed rocking non-prescription shades... in the rain... on New Year's Eve during a Slayer concert. With that kind of context, the absolute importance of "Keeping It Simple, Stupid" in Mobile UI design becomes painfully obvious; and your app's UI should be so easy, it's torturous. Consistent placement, clean layouts, intuitive pathways & juicy rewards pave the way to happy users - not to mention a well fed bank account.