Christ famously taught that “all have sinned and fallen short of the glory of God.” What needs to be pointed out is that we need not revile ourselves, we need not hate ourselves or others. Certainly, we need not judge others. What we need to understand is that if we were already relatively perfected, we would not exist on this planet at all. The simple fact that someone is HERE, ALREADY implies a relative lack of spiritual development. This is a remedial education camp.
Sin is separation from God, which happens when we fall short of hearing the call of the best within us, when we cloud our true perceptions with rationalizations, and emotional coverups, to justify doing what is expedient but not right. Life on this planet is already separation from God, who is much harder to see here.
These are my intuitions. I want to be clear that I base them in part on experiences I have had, but in part as well on things I have simply read.