It is a comment about how large projects, at least from my experience, seem to use complex data structures that takes several indirection to follow.
In both C and python I have also see something akin to a mini language inside the large projects, where understanding the code becomes almost impossible without documentation. In C, both macros and pointers to structs with more pointers can do a lot of heavy lifting to hide every detail of how something is being done and just leave the intention. Great if one want to see a high level concept and creating new features, but terrible if you want to know where that one bit of information is being stored and how to inject your own code into the core parts of the project. Similar, large projects in python tend to use meta, monkey patching and other dark magic patterns to really hide the low level details while making it easy to create new features.
In both C and python I have also see something akin to a mini language inside the large projects, where understanding the code becomes almost impossible without documentation. In C, both macros and pointers to structs with more pointers can do a lot of heavy lifting to hide every detail of how something is being done and just leave the intention. Great if one want to see a high level concept and creating new features, but terrible if you want to know where that one bit of information is being stored and how to inject your own code into the core parts of the project. Similar, large projects in python tend to use meta, monkey patching and other dark magic patterns to really hide the low level details while making it easy to create new features.