Ars longa, vita brevis
The original text, a standard Latin translation, and an English translation from the Greek follow.
The Latin translation is more clearly recognizable, but less idiomatic, using English terms descended from the Latin:
- Art [is] long,
- vitality [is] brief,
- occasion precipitous,
- experiment perilous,
- judgment difficult.
The most common and significant caveat made regarding the saying is that "art" (Latin: ars, translating Ancient Greek: τέχνη (techne)) originally meant "technique, craft" (as in The Art of War), not "fine art". Hippocrates was a physician who made this the opening statement in a medical text. The lines which follow: "The physician must not only be prepared to do what is right himself, but also to make the patient, the attendants, and externals cooperate." Thus in plainer language "it takes a long time to acquire and perfect one's expertise (in, say, medicine) and one has but a short time in which to do it". It can be misinterpreted as "art lasts forever, but artists die and are forgotten", in this use sometimes rendered in the Greek order as "Life is short, Art eternal", but most commonly it just refers to how time limits our accomplishments in life.
Related sayings 
The late-medieval author Chaucer (c.1343–1400) observed “Life is so short, and the craft takes so long to learn” (Parlement of Foules). The first-century CE rabbi Tarfon is quoted as saying "The day is short, the labor vast, the workers lazy, the reward great, the Master urgent." (Avot 2:20)