Modern learning science tell us that the biggest mistake in training is delivering too much information at one time. When too much information is presented, it sends the learner into the dreaded "information overload" zone (where information is only sent to the learner's working memory and eventually disappears).
When a learner is taught in this fashion, we are, in effect, stacking the learner’s short-term “working” memory. This portion of our memory has tremendous capacity, but it is limited. It will continue to fill with life’s other data ("Hey, I wonder what Bill is doing for lunch?" even during the training and within five days the average person will remember about 3% of your "very important" training session. Within 30 days the odds are the learner will only remember the lecture and likely none of the content (1).
But don't take it personally; evidence suggests that we are best at processing 1 - 4 chunks of information at a time—a chunk being a piece of information that supports a specific aspect of a learning objective. When we receive more chunks we do not have sufficient time to reflect and process the data. Now consider how many chunks are in the average lecture or a full-day training session. Yes, that means even those viral TedX talks we all love are not always the best format for delivering training.
YouTubers take note, the solution is not simply to produce shorter talks or shorter videos. The idea that shorter videos are better is not well understood. The key is not length, but to present content that supports a specific aspect of a learning objective. If you want a permanent memory the brain must process one thing at a time. In other words, size doesn't matter.
What if that one thing has several components? Design your content to teach the relatedness of those components—one component at a time.
What To Do Next:
Want to know what else modern learning science has to say about designing more effective training? Download sageCrowd's whitepaper The Brain's Natural Learning Cycles: Implications for Skill Development.