Hardship & Loss
The word "Islam" means "to surrender". The idea is that everything that happens is an act of God. When things start going bad, the devout Muslim can take solace in the fact that all is according to God's will and since God has perfect knowledge and is infinitely good, all that happens according to his will is good, whether or not we, in our limited understanding, may think so at the time.
This is a brutally effective reframing technique and it's my one favourite feature of Islam. I haven't seen studies on this and I'm not sure they'd be possible, but I can imagine the psychological benefits of this line of thinking are enormous.
The acceptance of that which we might think is undesirable is a common thread among many spiritual practices, but the only one I know of that focuses on it almost exclusively is Stoicism.
I am a big fan of Stoic philosophy, which teaches that virtue is freeing oneself from desires and to conquer our natural impulses that perpetually make us unhappy. Unlike Muslims, Stoics did not have a personified god, so they used terms like "Fortune" or "Nature" to refer to the prime mover.
By giving up desires and attachments, we can finally be free to surrender to whatever hands Fortune may deal. Whether it is losing our mundane, material possessions that we think are necessary for a happy life or losing a loved one, sooner or later Fortune will put us in an "undesirable" situation. The person with the mental fortitude to be unmoved by such challenges is the person who can truly live a peaceful life. Through meditation, Stoics try to strengthen their minds and reduce their attachments to things before they are taken away.
In many ways, I've tried to incorporate stoic principles in my life. I mostly avoid buying the kinds of nice things that many people are enamoured with. I typically don't care too much for my looks. I own very few things, and I sleep on a futon.
This is a good way to practice reducing one's attachment to things like material possessions or creature comforts, but denying oneself an additional pleasure that one does not already have is not the real challenge. The truly difficult task is dealing with loss of things or people that were precious to us.
Loss hits us harder than anything, and it is inescapable: death of a family member or friend, end of a relationship, or a life-changing injury or illness. However, whatever the loss you're coping with today, a bigger loss is always possible because the ultimate loss is death.
"Smaller" losses can be seen as opportunities for practicing mental fortitude that one will need when much bigger losses inevitably occur. The best case scenario facing any of us is that we get to live to an old age where our friends start dying one by one and when we start losing the most basic functions of our bodies.
The stoics believe that everything - the things you own, the people in your life, and your life itself - is a loan to you from Nature. One day (and that day may come much sooner than you expect), Nature will call in its loans. On that day, the person who has strengthened her mind will return to Nature what is hers not begrudgingly but with dignity and gratitude for the time she got to have with what was not her own.