Is it better to not even have a chance to work? Not sure why the choice has to be between a 100% effective solution and a "better than nothing" solution. It's

Is it better to not even have a chance to work? Not sure why the choice has to be between a 100% effective solution and a "better than nothing" solution. It's like saying to the Fire Extinguisher salesman, "But what if the fire is too big and I run out of propellant? No thanks I'm not going to own one."