Try doing some number crunching with engines where the manufacturers still haven't obtained an extension from 5 to 10 minutes after engine failure.
Much trickery can be involved when hills and other lumpy bits abound in great multitude! Particularly annoying to me was one "hilly" airport where the aircraft obstacle clearance performance was good, very good in fact, but it was necessary to impose an artificially steeper 2nd segment gradient to the higher than normal MAA to get there faster, reducing the 2nd segment time to leave enough of the 5 minutes for the 3rd segment.
Life wasn't meant to be easy
(with apologies to Malcolm Fraser).
Regards,
Old Smokey