Backsliding is avoidable, but only if we stay humble before God. We all need to "take heed, lest we fall". Pride comes before a fall, so don't over-estimate your immunity to failure. Some say that salvation is predestined, or predestinated, by God; we have no say in the matter. This is often referred to as the "doctrine of election" and it is used to support the concept of "assurance of salvation"