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.
(..) - And you are? - Am I late? - Yes, Mr. Sol. - Oh, good. Hi. - Sol. Richard Sol. - The burden of genius. - There he is. - So many supplicants, and so little time. - Mr. Sol. - How are you, sir? - Bender. (..)2001 A Beautiful Mind