Sforno on Deuteronomy 8:19/ספורנו על דברים ח׳:י״ט

1והיה אם שכוח תשכח, this will happen if you attribute your success to your own efforts instead of giving credit to G’d and thanking Him for it by blessing Him.

2תאבדון, you will be lost both in the terrestrial world and will forfeit your claim to eternal life after you depart from this earth.