"When a tenant has signed a two-year lease and then for some reason finds himself in the position where he has to leave, the landlord has an obligation to try to rent out the premises to someone else." Explain the accuracy of that statement.

Except where otherwise created by statute (which is often the case), a landlord has no such obligation. The tenant is obligated for the lease period, and if he chooses to leave earlier, that does not relieve him of his obligation to pay rent.