Related to Working memory is a performance-limiting factor and Everything is chunking, the ability to swiftly and reliably fall back onto a large corpus of internalized knowledge in long-term memory frees up cognitive resources to focus on associations between concepts, implications, and other higher-order mental constructs.
From Augmenting Long-term Memory by Michael Nielsen:
Over the years, I’ve often helped people learn technical subjects such as quantum mechanics. Over time you come to see patterns in how people get stuck. One common pattern is that people think they’re getting stuck on esoteric, complex issues. But when you dig down it turns out they’re having a hard time with basic notation and terminology. It’s difficult to understand quantum mechanics when you’re unclear about every third word or piece of notation! Every sentence is a struggle.
The more basic concepts one has available in long-term memory, the more tools they have with which to think. Each chunk in memory also represents another node in a graph of potential associations to make, the more chunks one has encoded the more novel associations they have the potential to make. Ease of recall decreases the activation energy required both to utilize long-term memory in cognitive tasks, as well as to form novel associations.