A surgical instrument , comprising: an end effector comprising a staple cartridge, wherein said staple cartridge comprises: a cartridge body; staples removably stored in said cartridge body; and a sled configured to eject said staples from said cartridge body; and a firing assembly comprising a mechanical firing force lockout mechanism , characterised in that said mechanical firing force lockout mechanism comprises: an intact state, wherein said firing assembly is configured to transmit a first load to said sled during a firing stroke when said mechanical firing force lockout mechanism is in said intact state, wherein said mechanical firing force lockout mechanism is in said intact state when said first load is below a predetermined force threshold and wherein said first load is a firing load; a first failed state, wherein said firing assembly is configured to transmit a second load to said sled when said mechanical firing force lockout mechanism is in said first failed state; and a second failed state, wherein said firing assembly cannot transmit a load to said sled when said mechanical firing force lockout mechanism is in said second failed state, wherein said first load is greater than said second load. an end effector comprising a staple cartridge, wherein said staple cartridge comprises: a cartridge body; staples removably stored in said cartridge body; and a sled configured to eject said staples from said cartridge body; and a cartridge body; staples removably stored in said cartridge body; and a sled configured to eject said staples from said cartridge body; and a firing assembly comprising a mechanical firing force lockout mechanism , characterised in that said mechanical firing force lockout mechanism comprises: an intact state, wherein said firing assembly is configured to transmit a first load to said sled during a firing stroke when said mechanical firing force lockout mechanism is in said intact state, wherein said mechanical firing force lockout mechanism is in said intact state when said first load is below a predetermined force threshold and wherein said first load is a firing load; a first failed state, wherein said firing assembly is configured to transmit a second load to said sled when said mechanical firing force lockout mechanism is in said first failed state; and a second failed state, wherein said firing assembly cannot transmit a load to said sled when said mechanical firing force lockout mechanism is in said second failed state, wherein said first load is greater than said second load. an intact state, wherein said firing assembly is configured to transmit a first load to said sled during a firing stroke when said mechanical firing force lockout mechanism is in said intact state, wherein said mechanical firing force lockout mechanism is in said intact state when said first load is below a predetermined force threshold and wherein said first load is a firing load; a first failed state, wherein said firing assembly is configured to transmit a second load to said sled when said mechanical firing force lockout mechanism is in said first failed state; and a second failed state, wherein said firing assembly cannot transmit a load to said sled when said mechanical firing force lockout mechanism is in said second failed state, wherein said first load is greater than said second load. <EOS>