The second Caliph of Islam, Umar Farooq gave a very unique advice. He said, that the sweetest sip is the sip of anger. 
What he said is literally recorded as "I did not sip anything sweeter than anger" (Kanzul Ummal, Hadith No. 8748) If you think about this - anger is a very bitter experience. When one is angry, one burns from within! 
An angry person wants to annihilate the one who provoked him. You know that anger is a bitter thing. Then why is he saying that anger is the ‘sweetest sip’? How is this so? I have thought a lot about why he equated anger to a sweet sip! I realized that anger gives us an opportunity to solicit a blessing of God. Because it is clearly cited in the Quran and Hadith that "those who restrain their anger …" (3:134). In other words, if you exercise patience, sip your anger and diffuse it within, this act will make you worthy of a great reward. 

What does this mean?
It means that the state for earning super reward is when you are angry! When you are calm, talk politely to others and no one has provoked you to get angry, it is not an opportunity! The opportunity arises when you can sip your anger, when someone provokes you and anger rages within you. Then you become worthy of super blessing. So Umar Farooq meant that when you rage with anger, it is an opportunity. He viewed anger as a very big opportunity. 
So one aspect of anger is that anger provoked you and invoked rage in you. But the other aspect is that if you sip the anger and diffuse the anger within you, then you can use it as an opportunity.