Question

Mistakes can be mistakes of which allow a contract to be voided or mistakes of which do not.

Answer 1

The question failed to provide the blanks spaces but I have come across this, here is the complete sentence with blanks filled;

Mistakes can be mistakes of "Fact", which allow a contract to be voided or mistakes of "Value", which do not.

For a mistake to discredit an agreement, it typically should be a shared one about a material actuality or fact. Rarely a one-sided mistake will discredit an agreement.