To limit the probability that the calculation of loads due to earthquake will not take into account the properties of the structural system [i.e. lack of ductility, energy absorption and overstrength], which could lead to structural failure, which could lead to harm to persons.
To limit the probability that the lateral-force-resisting system chosen for the design will not have a minimum ductility, integrity, and overstrength to absorb local failure due to maximum expected seismic ground motions, which could lead to structural failure, which could lead to harm to persons.