User experience design has evolved through five major eras—from Human Factors and the Web to Mobile, Design Systems, and AI—each contributing a lasting lesson while leaving behind habits that later became limitations. Designers should focus less on producing interfaces and more on shaping systems, information architecture, constraints, and the rules that govern intelligent experiences, as these are becoming the most valuable skills in the AI era. Rather than replacing UX, AI continues the historical pattern of making creation cheaper while shifting designers' value toward higher-level thinking and decision-making.