Parashat Shelah Lekha, which we are reading this week, features the tale of the twelve "spies" sent by Moses to check out the land of Israel while the Israelites are still wandering in the desert.
Ten of the twelve return with a bad report: the inhabitants of the land are fierce giants, and they would surely overwhelm the Israelites. Two of them, Joshua and Caleb, are optimists who declare that the Israelites should march into the land and take it. The storyline of the Tanakh (Hebrew bible) goes with the optimists; Joshua himself leads the people into the land.
No matter how bleak the future may look, no matter how many declare a particular task impossible, there is always a chance that the glass may be at least half full. It is always a good idea to listen to life's naysayers, just so that you might have the opportunity to prove them wrong. Say yes!