There's always been this notion that middle kids in the family have it the worst. They aren't the blessed first born who is praised for merely accomplishing things first (and these tasks can be as simple as going into high school or hitting puberty). Middle children are also not the precious baby of the family, the last hope parents have to raise a perfect human being. Along with that as the youngest child grows older and begins to move into adulthood, parents obsess over going through important parental duties for the last time, which leads to wails of, "my little baby boy is growing up."
Competing with these two siblings, the middle child typically doesn't receive too much attention, at least not in comparison. So what do middle kids have to look forward to? What advantage do they have over the other siblings?
Alone time
Having the least amount of parents' attentions can originally seem like a downside to being the middle kid. However, this means a lot of time without parental guidance. Middle children tend to be left to figure life out on their own, which ends up causing (in most cases) a strong sense of responsibility and independence. That's not to say that they are neglected by their parents, only that the parents devote less time to them than to their other children.
Getting out of trouble
Now, this does not work every time (maybe only five out of seven tries), but when all the kids get in trouble, the middle one can usually blame one of the others. The other two tend to be the center of attention, so parents' minds are already thinking of how the oldest and the youngest are involved in the situation. By placing the blame on one (or both) of them, the middle kid just gives parents more of a reason to think on those suspicions. The older kid is the better scapegoat in matters of responsibility, since they are expected to be the most mature, while the youngest should be given the blame for any other situation. The baby of the family is usually the most doted on, so their punishments aren't as harsh.
Playtime with both siblings
Sometimes, it's hard for younger siblings to spend time with their older brothers or sisters. Age differences lead to differences in opinions and interests. Luckily, middle children have the ability to bridge over those gaps. They are mature enough to not embarrass their older siblings in front of their friends, while also being youthful enough to enjoy playing more childish games with their younger siblings. In that regard, middle kids are like sneaky chameleons, blending themselves seamlessly into any group of people. This trick comes in handy in adulthood too, knowing when to be formal and serious or when to let loose and have fun.
So yes, there is this assumption that middle kids are given the worst lot, but in reality, the things that set them apart from the older and younger counterparts can actually give them an advantage.