The 'Desirable Difficulty' Principle
Psychologists often refer to "desirable difficulty"—the concept that slightly harder tasks lead to deeper encoding in the brain. Peak cognitive function doesn't last as long as many assume. Processing speed begins to decline in the late twenties, and working memory—the mental space where we hold and manipulate thoughts—starts fading in the thirties. By age fifty, these changes become noticeable, not just statistical.