Siddhartha even got married and started his own family, his life was going very well. But he started to become curious of the outside world, that he has never seen before.
When Siddhartha walked through the city, unattended from what his father wanted him to see. He discovered an old man walking by and saw a sick man laying on the floor. He became upset over what he saw.
Siddhartha walked outside of the city, to a village with poor people. He saw a corpse on the ground and it overwhelmed him with sadness. But he also saw an ascetic, abstaining from life's pleasures to find spiritual enlightenment, he decided to do that himself.