You got to be careful if you don’t know where you’re going, because you might not get there.

Yogi Berra (1925-2015) American baseball player, coach, manager [b. Lawrence Peter Berra]

(Attributed)

Variants:

• "If you don't know where you're going, you might not get there."
• "If you don't know where you're going, you'll wind up somewhere else."