Muslims should rely on Allah rather than themselves 9:25-27
9:25 Allah has helped you on many a battlefield. In the Battle of Hunain, when your numbers were pleasing you they availed you nothing; the earth, for all its vastness, seemed to close in upon you and you turned your backs and fled.
9:26 Then, Allah caused His sechina (tranquility) to descend upon His Messenger and the believers; He sent legions you did not see and sternly punished the unbelievers. Such is the recompense of the unbelievers.