when did gulliver realise that travel was his'fortune to do '?

After he finished at a Puritan college, Gulliver became an apprentice to a surgeon in London, during which time he also learned about navigation and mathematics in preparation for a future on the sea, "as I always believed it would be some time or other my fortune to do." Next he studied "Physick" (medicine) because he thought it would be "useful in long Voyages."