Why do students learn something and evidence it then a few months later completely forget it? Because they are using working memory to retrieve learning and we tend to assess using working memory retrieval (Block learning).
Our brains are designed to learn and forget what isn't 'important' or immediately useful. Interleaving and Spacing learning methodology helps our brain commit learning to long term memory.
Robert Bjork, Distinguished Research Professor in the UCLA Department of Psychology, shares insights from his work as a renowned expert on human learning. (can watch at 1.5x speed )