AngularJS is a prime example. Two-way data was a solved problem until people realized it wouldn&#x27;t scale.<p>Single Page Applications solve a lot of problems (ex better UX, offloading load from the server, better separation of concerns) but they introduce a lot of new ones (ex SEO, UI unresponsiveness, etc).<p>This is the steady and painful march toward progress. Add new functionality, identify the weaknesses, ditch the useless functionality, recycle the good parts and start again to test new assumptions.