From the Greek.

A man who was about to hang himself,
Finding a purse, then threw away his rope;
The owner, coming to reclaim his pelf,
The halter found; and used it. So is Hope
Changed for Despair--one laid upon the shelf,
We take the other. Under Heaven’s high cope
Fortune is God—all you endure and do
Depends on circumstance as much as you.

Percy Bysshe Shelley

http://www.poemhunter.com/poem/epigram-iv-circumstance/