The phrase "unbearable burden" means something that is extremely difficult or overwhelming to handle or cope with. It refers to a heavy weight or responsibility that feels almost impossible to manage. Full definition
Of course all this is incidental in respect of the larger matter that no British Christian leader really understands the aloofness of the United States in an hour when the world is staggering under an almost unbearable burden, and when the matter is put in this fashion the memory that Britain adopted just such an attitude of aloofness after the Napoleonic wars does not really constitute a defense of our position. (religion-online.org)
Even when small business loans are accessible, loan payments and interests can often be an unbearable burden for a startup. (entrepreneur.com)
He's the only one that understands that our Government is becoming a tyranny, and an unbearable burden to the People. (religion.blogs.cnn.com)