seventy-five years, he lived with his dad.. for seventy-five years, this man must have not even taken a field trip, or gone on an educational exchange..
in fact, the one time he actually went out on an extremely long excursion (from what is now, ur, southwest of nasiriyah, iraq to harran, turkey: roughly nine-hundred kilometers by traditional route), he was travelling with his dad, and it wasn't a field trip, or an educational exchange; it was a great migration.

Terah lost his youngest son, and that, probably wasn't a good thing back then. he (and others) probably saw that as a sign that his good days in ur were history. as a result, bad luck Terah probably had to leave.
my guess is that  as the eldest son, Abram had to go with his dad whether he wanted to or not. that was how it worked back then, and that still is how it works in some cultures even this day.

people often think that Abram left haran after his father died. but, the interesting thing is, Abram was born when Terah was in his seventies, and Abram left haran when he was seventy-five (meaning Terah was a hundred forty-five years old). Terah died at the age of two-hundred and five: when his eldest son left him, Terah wasn't dead yet! in fact, Terah died only two years before Sarah (his granddaughter and daughter-in-law), which means Terah probably saw Ishmael and Isaac(maybe once or twice at some huge clan gathering), and he most definitely saw Laban and Rebecca. Nahor didn't initally follow his dad to haran, but my guess is, after Abram left, word reached him in ur, and he probably came up to haran to do the elder son duties that Abram had left.

so, what was it that made him venture out in his seventies to a land that he knew so little of? what was it that captivated him to move on from his dad all of a sudden?
'blind' faith?