What motivated Europeans during the age of discovery

Although the Chinese and the Ottomans, among other societies, had the technology, wealth, and political stability to launch massive overseas voyages, it was the Europeans who took the lead during the Age of Discovery. Why? What was motivating Europeans? What was it about the international situation or Europe itself that impelled Europeans to establish overseas contacts while the Chinese and the Ottomans were content to let the world come to them? What do you think was the most significant factor? Why? Give specifics.