Published: April 25, 2026 When the past answer becomes the present problem, we call it Path Dependency. TCP was designed in 1981. It solved the right problems for its time. By the time HTTP was carrying the modern web, that 40-year-old foundation was starting to show its age. Keep-Alive solved the contract problem. One connection, many requests. Cheaper by design. But the queue was still single-file. Fix the engine, and suddenly the road is the problem. That road was TCP. HTTP/1.1 — One Lane, No Exceptions HTTP/1.1 had one rigid rule: one connection handles one request at a time, in order. Keep-Alive meant you didn't have to renegotiate a new contract for every exchange. But the delivery itself was still sequential. One large image delayed at the front of the queue, and every lightweight text file behind it had to wait. The connection was alive — it just couldn't move two things at once. This is Head-of-Line Blocking (HOLB) .…