A situation in which a building owner is unable to meet the operating expenses of a building because the building's income is less than the building's expenses. In co-operatives where the sponsor maintains unsold shares, there is a good chance that the tenants occupying unsold share apartments are paying below-market rents while the sponsor is responsible for the maintenance payments to the co-operative for the particular apartment. There is a tremendous likelihood that the difference between the collected rent and the maintenance due the co-operative can create a long-term financial burden for a sponsor. This is referred to as a shortfall. Obviously, the more unsold shares owned by a sponsor, the greater the financial strain.