Downplayed: Bob's parents are Put on a Bus or made useless. They're still alive but unable to truly interfere in Bob's adventures.
Justified: This is Crapsack World, Bob lost his father in war. And his mother was kidnapped when group of bandits raid his poor village.
Bob's parents are still alive, and he can't go on an adventure to collect the power crystals because his parent's say he can't.
Bob's parents are still alive, and the only reason he can go on an adventure is because they raised him to be the hero. If they'd died at any time before the quest, he could never succeed.
Bob's parents are still alive, but they are abusive parents who never care about him. So Bob going for adventure, promise them that he will bring back some money.
Alice is an orphan. The Hero adopt her and take her on adventuring.
His parents are killed off shortly afterward, allowing him to go on his adventure without return.
Not so long after Alice was adopted, The Hero is killed and Alice continue her adventure.
Parodied: Everyone is an orphan. Everyone in town? They're orphans. The Big Bad? Orphan. The protagonist and his friends? Orphans.
Zig Zagged: Bob has been led to believe his parents have been killed, and goes on an adventure to avenge them. During the course of his adventure, he discovers one or both of his parents alive and well and suspends his quest for vengeance. Shortly thereafter, his parent/s are actually killed and he must resume his quest.
Averted: Bob is not restricted to go on an adventure by his parents, who are alive.
Enforced: "His parents would never let him go on such a suicidal journey. We're going to have to kill them off."
"My parents are dead. Bye friends, I'm off to have a parental free adventure!"
"It's not as bad as you think, being an orphan. It's actually quite convenient."
Defied: Orphans are not allowed to go off to wherever they please, they have to be taken care of through foster care or placed in an orphanage, where they can grow up safely with proper supervision.
Discussed: "Shouldn't someone be supervising you, even if you don't have parents?"
Conversed: "He's an orphan because the writers couldn't think of any other way the kid could get around authority this blatantly.
Both of Bob's parents come down with a terminal disease. He can't go on his adventure because he has to take care of them, because no one else will. His mother passes away, then his father, his last wish being to stay in the village. Out of grief and respect, he decides he can't take his adventure.
The suffering of his parents' deaths, and the emotional neglect of the orphanage, have left Bob so emotionally traumatized that he can not form healthy relationships; he compensates by heroic deeds and Walking the Earth so no one gets too attached to him.
Reconstructed: Bob learns as time passes by that his father was actually an assassin, and didn't want Bob to leave the village because he didn't want his son to learn about his profession as a trained killer. Returning home after a failed mission with the police hot on his tail, he poisoned both himself and his wife. His realization of this, and the desire to learn about his father's life, gives him the courage to go out and find the power crystals.