I will break it down for you: The oldest was the first sheltered so has all the ability/skills of both parents. YOU (the middle child, moi) are then born and cannot hope to reach the ability of the oldest. Then the youngest comes along and, is not only pampered because he/she is "the baby," but also seen as the "new hope" because of the depression and lack of achievement you experienced as the middle and the rebellious attitude of the oldest (who became cocky because of his/her shitload of ability and decided he/she'd do things their way instead of the parents' way.) You, as the middle, are then left to fend for yourself because you're not the prodigy or the "new hope;" You're just... there. That's the middle child curse in a nutshell.
Unfortunately, many people think finding a case supporting their "truth" means it's a fact in most, if not all, situations. That type of stubborn thinking makes them no better than those who just believe what someone else tells them without fact-checking.