What is the meaning of [Put the saddle on the right horse]

Blame those who deserve it, not those who don’t.

> An author’s new book had been reviewed unfavourably in a literary weekly. He
said to an acquaintance:

> ‘I’ll concede that a critic has a right to give an honest opinion, but I
think John Cartright went a bit too far this time.’

> ‘How do you know it was Cartright? The article wasn’t sighed.’

> ‘I’d recognize his style anywhere, confound him!’

> ‘You’re putting the saddle on the wrong horse, old man. John Cartright
didn’t write that review. _I_ did.’