Vayetze: The Value of Self-Doubt

Yaakov leaves home to escape Esau, to find a wife. Filled with past fears, and trepidation for the future, God appears to him in the famous vision of the ladder with a message of reassurance. God promises:
“I am with you. I will protect you wherever you go and I will bring you back to this land. I will not leave you until I have done what I have promised you.”(28:15)
Jacob wakes in the morning, stunned by his dream and vows
“If God is with me, if He protects me on this journey that I am taking…”
If? Really? God had promised to protect Yaakov! Why is Yaakov doubting God’s assurance?
Ramban suggests that he is not doubting God; he is doubting himself:
“The reason for this conditional statement is that he was concerned that שמא יגרום החטא he might sin [and become unworthy of God’s promise]. Similarly, Rav Huna in the name of Rav Acha: From here we understand that there are no assurances to a tzaddik in this world