A failing type assertion that correctly fails because the input is not that type is good: it lets you divert to another path. E.g. if it's Type X do this, if it

A failing type assertion that correctly fails because the input is not that type is good: it lets you divert to another path. E.g. if it's Type X do this, if it's Type Y do that. Or even just put up a vaguely-useful error to the user: "The third-party service didn't send the expected data" instead of throwing the obscure error `Cannot read property 'prop' of responseData` in the console and freezing.