The 'burden of proof' is on the plaintiff, since the defendant is presumed innocent until proven guilty. [=the plaintiff must prove that the defendant is guilty]
The 'tax burden' has been falling increasingly on the middle class. [=middle class people have been paying a greater portion of taxes]
For the rest of his life he 'was burdened' with the knowledge that he had done nothing to help them.
(..) Ready, steady. Here we go and action. And we played the whole sequence out so Thorin, Richard, went up and hugged Bilbo. THORIN: Did I not say you were a burden? That you would not survive in the Wild? That you had no place amongst us? I have never been so wrong in all my life. Party group hug! (..)2012 The Hobbit: An Unexpected Journey