It's never reasonable although it doesn't stop people from doing it. History has shown us the folly of this (eg read "When Genius Failed" for a great history o

It's never reasonable although it doesn't stop people from doing it. History has shown us the folly of this (eg read "When Genius Failed" for a great history of the LTCM collapse). Due to multiple failures, large banks are to a greater or lesser extent prevented from doing this, but smaller financial players do get themselves into trouble.