"New research shows why it doesn’t take much for a new problem or an unfamiliar task to tax our thinking. According to University of Queensland cognitive science researchers …, the number of individual variables we can mentally handle while trying to solve a problem (like baking a lemon meringue pie) is relatively small: Four variables are difficult; five are nearly impossible. …
It’s difficult to measure the limits of processing capacity because most people automatically use problem solving skills to break down large complex problems into small, manageable ‘chunks.’ A baker, for example, will treat “cream butter, sugar and egg together” as a single chunk — a single step in the process — rather than thinking of each ingredient separately. …
The researchers found that, as the problems got more complex, participants performed less well and were less confident. They were significantly less able to accurately solve the problems involving four-way interactions than the ones involving three-way interactions, and they were (not surprisingly) less confident of their solutions. And five-way interactions? Forget it. Their performance was no better than chance.
After the four- and five-way interactions, participants said things like, ‘I kept losing information,’ and ‘I just lost track.’" [How much can your mind keep track of?]