“Whether you know it now or not, however, you have willed to cooperate in a concerted and very commendable effort to become both harmless and helpful, two attributes which must go together. Your attitudes, even toward this, are necessarily conflicted, because all attitudes are ego-based. This will not last. Be patient a while and remember what we said once before: The outcome is as certain as God!” (ACIM, COA ed., T-4.III.9:1-4)
So we are to be both harmless and helpful, an assertion that tells us how to interact with our brothers and sisters. We may sometimes become angry with them, but anger is not a sin, and when we regroup, we will realize a better way is to live and let live. Nothing more. We will not attack in retaliation, being harmless. We will seek proactively to be good to others, being helpful. These two words, harmless and helpful, give us a mantra to take us through our sometimes stressful days with our brothers and sisters.
We are going to make it back to God; the outcome is certain. Once the journey back has begun (and it has begun for all of us reading and writing this), the end is a clear thing, a certain thing (as Jesus tells us). We need not agonize that we are doing things all wrong, because we are doing the best we can at any given time.
And that is all that is required.