But.... This is one of the ways to get to like your character. You give them a few interesting details & a reason why they've taken up the adventuring life. You don't have to write something the size of War & Peace, just a paragraph or two.
So... I've been thinking about this particular thing a little bit, and it actually has come into play for a character that I've recently made for a campaign taking place in Waterdeep (the Forgotten Realms).
The more that I think about a character before play begins, the more of a jerk that character inevitably ends up being. People who go on adventures to thwart 'evildoers', mostly by the application of violence are, have to be, inherently broken. Broken people are not good people.
So, I was considering playing the Wizard, Wu, from Wa. I ended up with an excellent Int (17) and a good Cha (16)
That's as far as I had gotten, but for some vague notions of being a sort of friendly, zany fish out of water type character. But then, about a week before play was to begin, my DM wanted some backstory, "Who is your family? why are you so far from home?" that sort of BS. So I thought about it a bit... And the character turned into a jerk.
Wu's father was (is?) a successful caravaneer named Leeland Travels, following on the earlier success of adventurers like Volo, having opened up some trade with the far east. While away on business, Leeland took a bride, Wu An, whom he impregnated and brought home (somewhere in the Heartlands, or maybe around the Moonsea, I don't know that much about FR geography).
Wu An died in childbirth, and Leeland, needing to be away on business much (all?) of the time allowed Wu (actual name Leeland the Younger) to be raised, cared for, and taught by nanny's tutors, and other household staff. While these people were all nice enough, young Wu was never able to form a strong attachment to any of them, feeling that their 'affection' was purchased, rather than given.
When Wu's talent for magic was discovered, he was apprenticed to a local wizard, Larkin. Larkin was an adequate teacher, but sparing with praise, and about as affectionate as an alligator. While he was now able to engage in learning the fascinating and wondrous Art of magic, his personal situation went from merely lonely to pretty miserable. His desire to master his training was equaled only by his resentment towards his absent family.
When Wu finally came of age (about the same time that he mastered his first batch of first circle spells) he returned home for the first time in three years to find that his father had taken a new wife and had a new son. Wu convinced the household staff to evacuate the house, gathered up (stole) enough coinage to see himself on his way, and burned the entire house to the ground. Then he stormed off (fled) to the west, eventually making his way to the Sword Coast and to Waterdeep.
Shortly after arriving in Waterdeep, Wu met a prostitute that he has taken a fancy to. She is currently in a somewhat abusive relationship with her manager, though she says that it wasn't always this way. He has a cordial relationship with the staff at the boarding house where he lives, and he has made a few contacts among other low-level Waterdhavian wizards.
He does not know it, but several bounty hunters are looking to bring him back to (whereever) to a. explain to his hurt and angry father WTF and also to stand trial for arson. The bounty hunters that are looking for him on behalf of his father have orders to bring him back alive. Arson is probably a capital offense, however, so the bounty hunters that are looking for him on behalf of whoever is in charge do not have such orders.
Wu sees most relationships as transactional. He is friendly, but not kind, is most comfortable around servants and household staff. And He feels the urge to repay even imagined slights in kind. His short term goals are to make enough money to pay for his rent and other expenses, and to negotiate his prostitute friend's release from her obligation to her manager, probably via coercion or force, possibly through a straight up murder.
So... Now I have a character with motivations, contacts, a background, plot hooks, and all kinds of past trauma by which to make sense of him being an adventurer. However, a character that probably would have been Neutral Good or Lawful Good, if maybe a bit goofy, is now Lawful Neutral
at best and more likely Lawful Evil or Neutral Evil. Before, he would have done things because they were the right thing to do, or even because of why the hell not. Now, he's going to want to know what's in it for him.