Methods in C# are non-virtual by default and almost every class in the core libraries is sealed and the world hasn&#x27;t ended in .NET land.<p>I have definitely done some hacks to work around bugs in frameworks I&#x27;ve used. But I&#x27;ve <i>also</i> had to deal with users who broke <i>my</i> libraries or inadvertently wandered into the weeds because it wasn&#x27;t clear what things were and weren&#x27;t allowed.<p>This is one of those features where the appeal depends entirely on which role you imagine yourself in in scenarios where the feature comes into play.