The root cause: Robinson was born in the middle class, and his father often educated him with the philosophy of contentment, asking him to satisfy the status quo and not to go to sea. But the overseas world lured him like an irresistible attraction. He was ambitious and determined to give up his comfortable and mediocre life and set sail for the sea.

Specific reason: 1. He was born with an adventurous spirit and started his first voyage without telling his father. 2. The adventure of going to sea for the first time prompted him to go to sea for the second time. 3. The adventurous character prompted him to go to sea for the third time. Like adventure, fear of loneliness and excitement, he decided not to be a manor owner and live a quiet life, and went to sea for the fourth time.