In Gulliver's Travels by Jonathan Swift, what makes Gulliver leave his house?

Gulliver leaves his childhood home in Nottinghamshire in order to acquire an education.  He attends a school in Cambridge called Emanuel College from age fourteen to seventeen.  After this, as the third of five sons, he is sent to be an apprentice to a doctor in London.  He studies as much as possible, but he eventually leaves this home in order to continue his formal education in medicine at Leyden.  When he returns to London, he leaves home again, at the suggestion of the man he had formerly apprenticed, in order to be the doctor on board the Swallow, a ship on which Gulliver travels for over three years. 
Later, after Gulliver marries and sees his medical practice fail, he leaves home to go to sea again and travels for six years more.  At this time, he determines to remain at home, but when he cannot make another business work, he goes, again, to sea, and thus begins his journey to Lilliput.