Its just all about the middle child itself...Whether he/she look things at a bright or darker side..

Its very normal since your a middle child, your older siblings usually will behave more matured compared to you so your parents would always use them as a reference for you...

And for the younger siblings they always gets more attention from your parents, not because they are more matured but just that they need more attention because they are younger.
Im sure when you were borned that time your parents will give more attention to you compared to your elder siblings so its the same concept here.

So as a middle child, you have to face maturity and act/behave like your older siblings and also since your not the youngest anymore then you should start behaving matured