For example, no one reading this letter can guarantee that they will be alive the next day.

ECONOMIST: When I'm 64

In recent days, students at Duke University, Apple CEO Tim Cook's alma mater, published an open letter calling on Cook and Apple to guarantee "conflict-free" products.

CNN: Apple, consumers must urge worker justice

Gennady Onishchenko, Russia's chief sanitary official, told Ekho Moskvy radio that he has sent a letter to the European Commission requesting a guarantee that meat products sold to Russia don't contain horse meat.

NPR: Russia Seeks EU Guarantees Over Horse Meat Scandal

No PR firm can guarantee you editorial stories, but good publicists craft your press release or pitch letter (less formal presentation) to interest the media.

FORBES: By Robert Wynne

Seven letter bombs were sent over a period of three weeks and the police have warned that they cannot guarantee that there will not be another one.

BBC: NEWS | UK | Letter bomb suspect is arrested