The Battle of Uhud
[3:152] GOD has fulfilled His promise to you, and you defeated them by His leave. But then you wavered, disputed among yourselves, and disobeyed after He had shown you (the victory) you had longed for. But then, some of you became distracted by the spoils of this world, while others were rightly concerned with the Hereafter. He then diverted you from them to test you. He has pardoned you. GOD showers the believers with His grace.
[3:153] Recall that you rushed (after the spoils), paying no attention to anyone, even when the messenger was calling from behind you. Consequently, He substituted one misery for another, that you may not grieve over anything you had missed, or agonize over any hardship you had suffered. GOD is Cognizant of everything you do.
The Battle of Uhud was the second battle that the believers had against the disbelieving Meccans. The first was the Battle of Badr. During this battle the believers left Medina to encounter the Meccans at the Uhud Mountain. The believers were severely outnumbered, but because of the terrain were able to narrow the amount of Meccans that could engage in battle at a time by being shielded by the mountain. To protect the believers from being attacked from behind the messenger had some archers stationed at the adjacent mountain.
When the battle began the believers quickly won and caused the disbelievers to flee. This allowed the believers to gain in the spoils of the fleeing disbelievers. Some of the archers who saw this abandoned their post to go after the spoils. In doing so this left the believers vulnerable from an attack from the rear which the disbelievers took advantage of and therefore caused a lot of casualties among the believers.
Those who left their post had to face the death of their comrades with a lot of shame and grief as they felt responsible. Those who did this therefore substituted one misery (the missing of the spoils of war) for another (that that their defiance caused the death of their comrades). This loss made them forget about their original hardship.
Was this event and outcome good or bad for these individuals?
It is dependent on the individual either they will learn and grow from this situation and have their faith strengthened or have regret, doubt and lose trust in God.
God was controlling everything and allowed this event to happen in accordance with His plan, and this will raise some and lower others.
God Is Doing Everything*
[8:17] It was not you who killed them; GOD is the One who killed them. It was not you who threw when you threw; GOD is the One who threw. But He thus gives the believers a chance to earn a lot of credit. GOD is Hearer, Omniscient.