Diagrams help put things in context. Learners can draw on a sense of space to place things in relation to each other, improve recall amd understand a complex system as a whole.
Here are the diagrams from The Decision Book stripped of their content. Can you repurpose them to explain something? With a bit of practice, you'll be able to improvise great diagrams, simplifying disparate concepts.
"Simplicity is complexity resolved." - Eric Schmidt