At my old company one of my colleagues introduced async / await into our csharp code. He created interfaces and showed us a great structuring of his code. Sadly a few weeks later he left the company, because of personal reasons and a bug appeared in his written service. Our senior developer took the issue and complained for like 1 week. That you can't find anything, that interfaces are useless, that async / await is slow and sucks and that we should stop trying to bring new structures into the code base and do things the old way. In the end he deleted all the great things that my colleague introduced and wrote bad and smelly code.