  The extensive grid of numerical simulations of nova eruptions of Yaron et
al.(2005) first predicted that some classical novae might deviate significantly
from the Maximum Magnitude - Rate of Decline (MMRD) relation, which purports to
characterise novae as standard candles. Kasliwal et al. (2011) have announced
the observational detection of an apparently new class of faint, fast classical
novae in the Andromeda galaxy. These objects deviate strongly from the MMRD
relationship, exactly as predicted by Yaron et al. (2005). Shara et al. (2016)
recently reported the first detections of faint, fast novae in M87. These
previously overlooked objects are as common in the giant elliptical galaxy M87
as they are in the giant spiral M31; they comprise about 40% of all classical
nova eruptions and greatly increase the observational scatter in the MMRD
relation. We use the extensive grid of nova simulations of Yaron et al. (2005)
to identify the underlying causes of the existence of faint, fast novae. These
are systems which have accreted, and can thus eject, only very low mass
envelopes, of order 10^-7 - 10^-8 Msun, on massive white dwarfs. Such binaries
include, but are not limited to, the recurrent novae. These same models predict
the existence of ultrafast novae which display decline times t2 as short as
five hours. We outline a strategy for their future detection.
