With every interaction, users must overcome the twin challenges of understanding the current state of a system and figuring out how to change it. Designers can support them by being aware of these gulfs and bridging them with a transparent conceptual model.
Flat interfaces often use weak signifiers. In an eyetracking experiment comparing different kinds of clickability clues, UIs with weak signifiers required more user effort than strong ones.
Flat design is a web-design style that became popular around 2012. It is still widely used today, and its overuse can cause serious usability problems.
Whether you adopt a flat-design style or not, interactive components must retain sufficient cues to suggest clickability. Signaling clickability with cues such as borders, color, size, consistency, placement, and adherence to web standards can give interactive components the proper look.
iPad apps are inconsistent and have low feature discoverability, with frequent user errors due to accidental gestures. An overly strong print metaphor and weird interaction styles cause further usability problems.