Before 1935, all the front-line fighters in US inventory were biplanes. Just ten years later, we had gone to jet fighters.
Somethings we can predict but not do at the time but when the technology catches up the advances happen with amazing speed.
A lot of our stealth tech was well understood and in many cases tested back in the 50s. It was computers with processing power to make the constant adjustments that made those planes into stable flight platforms. Now things look like science fiction compared to when we saw the first stealth fighters.