In the early part of the scientific revolution, Francis Bacon said:
Man cannot do what has never been done, except by means not yet tried.
My understanding is that there are two parts to this; the means and the ends. Succeeding means getting both parts right. The fact that a field is littered with failed attempts doesn’t mean that the aim is unobtainable, or not worth obtaining. Nor does it mean that unconventional thinking is the key to success. It can just as easily be the key to new varieties of failure.
What it does mean, I think, is that taking conventional approaches to unsolved problems is a sure way to fail before you’ve even begun.