Of course time-to-learn should be taken into account. A mobile app which typically has a minimal number of options should not waste the user's time by teaching

Of course time-to-learn should be taken into account. A mobile app which typically has a minimal number of options should not waste the user's time by teaching things that are contrary to what they have learned in the host OS. Aesthetic options can be time-wasting. For example, the current fad of flatness (which ignores our innate capability to recognize depth from gradients) has made almost all the apps i use slower to use by forcing us to read every button.