Blockbuster could have bought Netflix for $50 million in 2000. Reed Hastings and Marc Randolph flew to Dallas to pitch it and got laughed out of the room. Cisco heard Eric Yuan's idea for a mobile-first video app, said no, and watched him leave with 40 Webex engineers to build Zoom. Excite passed on buying Google for $750K. Same pattern every time. The winners on this list all entered at the exact moment the market leader was maximally committed to something about to stop working. Blockbuster…