This document discusses challenges with concurrent programming as the number of threads increases. It notes that while multi-core processors allow for many threads, directly using a single linked list with many threads can cause problems. It introduces some concurrent data structures and synchronization methods like CAS, MVars, and STM that aim to provide atomicity, but each has limitations. Lazy immutable values and built-in atomic reads may help avoid some scaling issues as the number of threads approaches the number of cores.