This may have been Kennedy's most unforgivable error. The most remarkable thing about Dallek's book is its detailed cataloging of JFK's vast array of illnesses. It is amazing that JFK lived into his 20s, much less that he could keep his cool under the tremendous, nearly nonstop pressures of the years when he was president. Knowing of his extreme fragility, JFK was grossly irresponsible in not keeping his vice president (i.e., his not-at-all-unlikely successor) better-informed of his views.