Genesis 12:4

Since Lot voluntarily chose to accompany Abram, he probably believed the promises as well (cf. Ruth). Abram’s call had been to separate from his pagan relatives, so he was not disobedient by allowing Lot to accompany him. [Note: See ibid., p. 207.]

Probably Abram viewed Lot as his heir (cf. Genesis 11:27-32; Genesis 12:4-5; Genesis 13:1-2).

"Since Mesopotamian law-codes allowed for the adoption of an heir in the case of childlessness, this becomes an attractive hypothesis with respect to Lot." [Note: Helyer, p. 82.]

Abram lived 75 years with his father, then 25 years without his father or his son, and then 75 more years with his son, Isaac.