Why was parallel development not meaningful before the 2025 capability leap, even with products like Cursor and CodeBuddy?

Before the leap, all solutions relied on a human-as-driver, AI-as-co-pilot model. Humans still had to manually review code, negotiate requirements through multi-turn conversations, and direct architectural decisions. Even if you opened five Agent windows, they all waited for your serial input. True autopilot hadn't arrived—parallelism just turned a single queue into concurrent queues, all blocked by the same human bottleneck. The article explains that only when mechanisms can independently handle debugging, correctness, and maintainability does parallelism become effective.