The meraglim (spies) were lacking in their faith and in a clear understanding that ultimately Hashem wants what is best for us. This fault of the meraglim is traced all of the way back to Adam's original sin in Gan Eden. Chava listened to the words of the snake, although they opposed Hashem's words. So too, the meraglim came with reports that opposed the word of Hashem. We must be careful to always listen to the word of Hashem, without listening to the Yetzer Hara or other forces that try to tell us otherwise.