A biography for Vladimir I. Arnoldhasn’t been written yet.
“... for systems belonging to the singular part of the stability boundary a small change of the parameters is more likely to send the system into the unstable region than into the stable region. This is a manifestation of a general principle stating that all good things (e.g. stability) are more fragile than bad things. It seems that in good situations a number of requirements must hold simultaneously, while to call a situation bad even one failure suffices.”