Cognitive load is the total mental effort required to process your page. Every element — text, images, animations, navigation options, color choices — consumes a portion of the visitor's limited processing capacity. When that capacity is exceeded, visitors default to the easiest action: leaving.
George Miller's research established that working memory can hold about 7 (±2) items simultaneously. More recent research by Nelson Cowan suggests it's closer to 4. Your page is competing for those 4 slots against everything else the visitor is thinking about.
How high cognitive load manifests on landing pages
Too many choices: Hick's Law states that decision time increases logarithmically with the number of options. A page with 5 equally prominent CTAs takes longer to decide on than a page with 1 clear primary action. The visitor may decide by not deciding — and leaving.
Complex language: Studies by Hyunjin Song and Norbert Schwarz showed that information presented in easy-to-process fonts was judged as more truthful. The same content, literally the same words, was rated as more believable when it was easier to read. Clear writing isn't just good UX — it's a credibility signal.
Visual clutter: Every element on the page that isn't directly supporting the conversion goal is adding cognitive load. Decorative elements, animation, excessive imagery, busy backgrounds — each one costs processing capacity that could be spent understanding your value proposition.