In construction, there are “weight bearing” support structures – if this support is knocked down or otherwise compromised, the whole building can come down on your head. Also, if you “overload” these weight-bearing supports with two much weight… well, same thing can happen. Obviously, this is a Bad Thing.
I have recently discovered a similar principal in UI design – each screen, based on its purpose, has a “bearing weight” it can maintain before failing the users. Let me explain:
I recently designed and tested three types of screens, and two of the screens tested well – the participants understood what the screen should do and were able to accomplish tasks with no questions or problems. The third screen was different. Users looked at this screen and were completely lost. They understood, to some extent, what they could “do” in the screen, but they did not know where to start.
It was cognitive overload, due, to a great extent, to exceeding this screen’s “bearing weight” – there was too much to process, and the participants “shut down.”
Was this the primary cause of the participant’s confusion? No – there were other usability issues observed and factors at play (for example, a different layout from the two “sister” screens was used). But the fact that it had one module too many was important, especially looking at the intended use of the screen.
It was a forecasting/analysis screen that users would be able to access to do planning activities. Several sections of the screen DID NOT SUPPORT that task, and this extra “cognitive baggage” it reduced the total usability of the whole UI.
Naturally, this “bearing weight” of any UI will vary based on context and purpose – the screen for a mobile application, or a log-in screen, may have a “single-threaded” task that should have no distractions or additional design elements – it’s “bearing weight” is low, one widget at most. The opposite end of the spectrum could be software stock brokers use to track the market ““ these users want as much information as the screen can provide, and therefore the screen can “bear” a lot of content areas and/or functional modules.
When in doubt, start simply, and then add layers of complexity based on design reviews and usability testing. Just as architects have to make sure the proper materials are used when planning weight-bearing walls, application designers must also find the right combination of functionality and content to make the screen work – without it crashing down on the user’s head.