Sasuke, for example, awakened his Sharingan after witnessing the death of his clan and Obito got his eyes due to his immense resolve to protect his teammates in the third great ninja war.

When Itachi was a traumatized child soldier ... After a horrible accident crushed his body, he gave his Sharingan eye to Kakashi. But Obito didn't pass away. Instead, he was found by his ancestor ...