How Muslims can win? Umar's advice to the Muslim Army:

How Muslims can win? 

Umar's رضي الله ﺗﻌﺎﻟﯽٰ عنه advice to the Muslim Army:

‘Umar Ibn Al-Khattaab said (advising Sa’d Ibn Abee Waqqaas, who was the leader of an army):

“I urge you and the troops who are with you to fear Allah in all circumstances, for fear of Allah is the best means of preparation to face the enemy and the best plan at times of war. I command you and those who are with you to be more cautious of sin than of your enemy, for the sins of an army are more alarming for them than their enemy. And the Muslims are only granted divine help because of their enemy’s disobedience towards Allah.” 

[Al-Faarooq ‘Umar Ibn Al-Khattaab, by Muhammad Rasheed Rida, p.119]

This can equally apply to other areas of life and not just for fighters.