Skeletons in the closet? Make a clean sweep right here.
Some siblings keep secrets with such skill that an MI5 officer with advanced interrogation training would be impressed. Others can't keep it buttoned for more than five minutes.
When it's good
Talk to your friends and think about your own family, and you'll quickly find examples of people who are keeping all kinds of information hidden. Brothers and sisters the world over enjoy a good conspiratorial laugh about stuff that happened when they were younger, and they've kept quiet about for years. These are usually pranks like cutting off the family cat's whiskers, getting into minor scraps at school, or stealing sweets. Does everyone really have to know about everything? Probably not. No real harm done.
If they can keep something confidential, it's a sign that your brother or sister is also a good friend, and cares about your feelings. Knowing that you can really trust someone often gives you a strong sense of security. Siblings may be much closer to one another than they are to their parents or carers, and it's completely understandable if they are of similar ages and have lots in common.
When it's bad
Sometimes it can be a bit one-sided, with one sibling offloading all their personal problems and gossip onto the other one, then swearing them to secrecy. Without the usual amount of give and take, the person who keeps all the secrets can end up feeling overwhelmed and stressed out.
If there are problems with the parents, such as divorce proceedings or financial difficulties, their kids can sometimes end up worrying about upsetting their parents unnecessarily, so they might end up keeping information and problems amongst themselves.
There are times when a confidence may need to be broken too: when someone is being abused or bullied, is in trouble with the law, or has mental health problems, for example. The person who lets the secret out may end up feeling guilty and ashamed, and the other one can feel hurt and betrayed, even if they secretly know that they need more help.
When it's not a secret
Some brothers and sisters are only too happy to blurt out whatever you've just confessed to them, especially at an awkward moment. You get the little tittle-tattle, often a younger sibling, who runs off to the parents with every tiny detail as soon as the coast is clear. They're usually desperate to gain the attention and approval of your parents, rather than trying to get one over you. In many ways, this demonstrates that they're the one with the issues, and not you, so aim to steer clear from any kind of retaliation.
You also get the foghorn-gobbed sibling, who picks the most humiliating time to reveal your secret, and probably embellishes the story as well. The tiny spot on your bum, the one that you wanted to borrow the antiseptic cream for yesterday, becomes a gigantic abscess plus genital warts when they broadcast it. They will happily do it in front of elderly relatives, your mates, or some cute person you have your eye on. Again, your first instinct might be to punch them, but think twice about doing so. Indeed, they are a different kind of saddo, someone who thinks that putting others down will make them look better by comparison. Laugh it off, or come up with an even more stupid story yourself.