an emotional scarring condition.
Middle children are known for ending up with the things that are too big for the baby in the family and too small for the oldest.
it is a known fact the youngest and oldest are treated differently than the middle child for the oldest is the first child aka favorite
and the smallest is the baby aka the last child known for getting whatever they desire because they are the "baby"

Middle Children sydrome includes
neglect, forgotten dates, and sometimes in bad cases forgetting they even exist.

i lived through this condition,
it is not fatal
just difficult.

A disposition that generally arises with the middle child of three children in a household. Middle children often lack the attention that the oldest (the most important child) and the youngest (the parent's favorite child) receive.

Middle child syndrome is often characterized by: lack of friends (a loner), inability to maintain relationships, extreme creativity (writing, music, art, etc.), an easy going personality, trouble choosing a career path, trouble maintaining a career, quick loss of interest in things, negative outlook on life, half-assing, and indecisiveness. Famous middle children include David Letterman, Madonna, and Richard Nixon. Need I say more?

When a middle child - typically of a family of three kids who are close in age - feels left out or neglected.

Because the bigger sibling is the first born and typically an over-achiever, they are the most important and get the most privileges. A younger sibling is the 'baby' of a family and gets away with more as well as being the most looked-after. Middle-child syndrome starts when the middle child is squeezed between these two and have trouble finding their 'niche' in the family.

Middle children will sometimes...
-misbehave to get attention
-go with the flow
-work as little as possible
-be less parent-dependent then their siblings
-become the 'loner' of the family, not participate in family events unless told to.
-play the peacemaker
-be more likely to go to a friend for advice than a parent
-be very creative

In short its where the older child gets all the awards, the younger gets all the love, and the middle gets nothing.