Did they have middle child syndrome? 

Splinter had tried hard to treat all his sons equally, but it wasn't that easy. 

Leonardo shadowed everything he did, and Michelangelo needed more attention because he was easily distracted. 

Raph didn't like Leo spending time with Splinter instead of them. And he never understood why Mikey needed special treatment. He’d stolen time with their father by rebelling and lectures about his behaviour. 

Donnie had never tried to compete for his father’s attention. He worked on learning how to help his family instead.

He’d learnt to let his brothers keep the limelight to themselves.