While there is a temptation to "do something" just because someone is sane enough to recognize that an approach is doomed to failure doesn't mean they have all

While there is a temptation to "do something" just because someone is sane enough to recognize that an approach is doomed to failure doesn't mean they have all of the answers. I have seen that asserted but I haven't heard explicit answers. Why do you or others think it isn't tennable? How do you think it will collapse with lack of action?