Grief, in Arabic ghamm, occurs due to misfortunes that happened in the past, whilst worry, in Arabic hamm, occurs when one expects misfortune in the future.
When we have a feeling of grief in regards to our past sins, this feeling is of benefit to us and we will be rewarded for it. If we worry about a good deed that we wish to do, our worry will benefit us as well. However, if we grieve excessively for something that is lost in this world, then we should remind ourselves that what has been missed will never return, and that this type of grief only harms us.
A resolute person should protect themselves from what brings about grief, and that is losing objects that they love. If we have many objects that we love, our grief will increase if we lose them, but if we decrease our love of objects, we have less to lose. Someone might say, when I have no objects to love I still feel grief. This is true, but your grief over not having them is less than the grief of having them and then losing them. Just as the grief of the one who does not have a child is less intense than the one who has had a child and lost it.
When we be accustomed to things which we love for a long period of time, they take over our hearts and we feel reluctant to be parted from them. This will cause us to cling onto the life of this world, rather than desiring the next one.
The cure for these affliction is to remind oneself of the Qadr of Allah and that whatever He has predestined is going to happen. Know that this worldly life is founded on distress, all constructed buildings shall eventually be ruined and all gatherings shall eventually depart. Nothing is permanent.
Try and imagine what it would be like if what has befallen you were ten or one hundred times worse, this should make the suffering feel easier. It is the habit of smart porters to put something heavy on top of what they are carrying, and then, after taking a few steps, they remove that object so that the load feels lighter.
If we are in a time of prosperity, we should expect that tribulation will befall us, and when it comes we should focus on what we have remaining of what we had before, not what is lost.