Has anyone been flabbergasted that your sibling is related to you?

While it may be the harmless astonishment of an observer, it can be a more interesting conversation when your personalities - as siblings - are completely different.

This often begs the question: how does it happen that siblings can grow up under one roof and get afforded the same opportunities, yet turn out completely different when it comes to their life choices and personalities?

Sthembiso* spoke to us on condition of anonymity for fear of embarrassing his brother, whom he says he has nothing in common with.

The 32-year-old businessman runs a furniture shop in Kramerville, Sandton, but says his 25-year-old brother has had run-ins with the law, is unruly and disrespectful, steals from their mother and is the cause of a lot of conflict and tension at home in Chiawelo, Soweto.

"We grew up with loving, married parents. My dad, who passed away in 2008, was a hardworking guy who tried his best to provide for us.

"He wanted us both to get an education and not end up working as hard as he did at the mine. Being the older brother, I finished high school first and did my business management course.

"My brother on the other hand never showed any interest in studying and failed a couple of grades, and when it was his turn to further his education, he simply refused. He started smoking and drinking, something that none of our parents ever did.

"Most of the time I genuinely ask myself who he took after, because none of us at home have his personality."

Educational psychologist Nombulelo Nzama says that in extreme cases like Sthembiso's, people should be careful not to dismiss issues such as not having anything in common with a sibling, but instead realise there could be an underlying issue.

"We see cases like this all the time, where the one child is singled out as being the black sheep of the family based on some unbecoming behaviour.

"There are a lot of reasons why siblings usually take different paths when it comes to interests and personalities, but I want to encourage people to not paint one sibling with black paint based on unruly behaviour, without investigating the root cause.

"Sthembiso mentioned that their father passed away, and we don't know how that affected his brother.

"We don't know if the brother was bullied at school or genuinely felt inferior to his brother, especially in his parents' eyes.

"I would encourage a psychological intervention, where his brother could start to unpack and unravel the chronological events of his life until he unplucks the thorn that may have pricked him at some point, and hopefully heal from it," she says.