The secret of salvation tells you "you're doing this to yourself". ACIM also tells you "you but accuse your brother of your own sins." It also tells you that you "look within first" and then project outward, producing perception.
So the thing is, you START by attacking yourself first, accusing your self of sin. Then you look within. Then you project your own sin out. Then you find yourself in a situation where you seem to have to "forgive someone else", or at least begin the process of realizing it's not about them, taking back the projection, and then looking at why YOU are innocent.
But really most of the time we spend in undoing all this projected crap, it's not really even the original problem. The original problem is that we do not love ourselves. We attack ourselves. We have judged and condemned ourselves. We've believed ourselves to be unworthy of love and forgiveness. And it's only later that this becomes projected onto the world and other people, which produces a mess we have to then clean up before we can even home in on the real issue.
If you think about it, your only job then really involves the forgiving of YOUR SELF, which would automatically remove the need to project sin onto others in the first place. Your SELF ATTACK needs to be undone, in order to have no sin TO project. And if you are not experiencing love, it is because you have not forgiven YOUR SELF. You have blocks to the awareness of love's presence because you do not believe you deserve to be loved. You don't love other people because you hate yourself first.
Forgiveness is not really complete until you return to a state of love, whether it seems to be about another person or yourself. Only when you can love the person that was an enemy, are you fully done forgiving them, and now welcome them with open arms. If you do not love yourself, it's because you have not forgiven yourself fully. Which means that you have grievances against yourself. You have beliefs about your own sinfulness. You are convinced of your own unworthiness and are hurting yourself.
If you were to address this actual problem, this inner self hatred, this suicidal self-abuse, the secret sins and hidden hates, not even on a basis of feeling guilty about accusing your brother of it, it would clear everything up. Jesus says you don't have to seek for love, you just need to remove the barriers you've built against it. Those barriers are barriers against YOU, against loving yourself. They are within you. And it's only later that you project them as a hellish world in ways that interfere with your relationships.
You are the one who needs to forgive, and you are the one who needs to be forgiven. By yourself. You need to learn to stop unloving yourself. You need to find out all the ways that you do not love yourself or are unwilling to do so. And they will indicate all the ways that you do not want to love others because YOU do not believe YOU deserve to receive love. And then you need to undo that belief so that you can recognize your entitlement to love.
Miracles function by applying to both YOU AND another. And so your unwillingness or inability to love another is only evidence of your unwillingness to love yourself. You would have to love yourself at the same time as loving them, and so you do not love them, because to love them you'd have to love yourself. And so you hold back your love of others because you don't want to love yourself. You are unwilling to love yourself because you hate yourself. And Jesus tells us not to underestimate the sheer extent of this hatred.
Ultimately though, the key is, that by recognizing you do this attack to yourself, the secret of salvation can offer you a way out. By healing your relationship WITH YOURSELF, by allowing yourself to receive love, by loving your own self first, you will automatically see the world differently. You will see a forgiven world only because YOU are forgiven. You will see forgiven brothers only because YOU have forgiven yourself. You will see a reflection of God in the world ONLY because within you you have no sin and guilt and God (love) is accepted as present in your mind, and so is projected onto the world.
It seems incredibly simple when you get down to it. So much ego time is spent lost and confused and caught up in external problems and other people and dramas and all these projected forms of your own self attack, such that it makes it seem most of the time it's not even about you. But its ONLY YOU that needs to get healed FIRST, to accept atonement FOR YOUR SELF, so that you can in turn be available to heal and help others. To offer love to them, you have to have love to give, and you can't have love to give when you don't acknowledge your own lovability.
You don't even really need to deal with trying to "forgive others" or to "forgive the world" or to "be more loving toward people". What you really need to focus on is getting your self to be more loved, by YOU. To find out why your relationship WITH YOURSELF is broken. To find out why and where you hate yourself, how you are denying yourself, and why you don't want to admit to being God's beloved child. All the rest is an ego distraction and a form of denial, an attempt to pass the buck and make the problem be outside your mind so that your own self attack remains hidden.
When YOUR mind gets corrected, your PERCEPTION will get corrected too. "Perception is a RESULT, not a cause". Perception doesn't even need to be "worked on". There is a massive amount of distraction with people thinking that they have to fix and shift their perception. You cannot DIRECTLY shift perception because it is a SIDE EFFECT. Spiritual perception is a RESULT of fixing YOUR BELIEFS about YOURSELF. It's what you sense AFTER you have looked within and have projected your inner world outward. As a man thinketh, about himself, so does he perceive.
This is all an inside job. YOUR MIND has shit in it that needs healing. All the world related to your self and the healing of yourself is entirely within you. You can use holy relationships or guidance or whatever else help along the way but ultimately, simplifying it greatly, Jesus is just asking you to 1) get yourself back to love and 2) then you'll share that love with others automatically.
Love goes out automatically because of its nature, and you don't even need to make it do that. It has its own function to do that. You just need to stop blocking it. And you do that by forgiving yourself for what YOU have not done. When you see your own sinlessness you'll see the sinlessness of your brother. When you see your own innocence you will see his. Once you do that, the rest will take care of itself. Seek the Kingdom of God within you and the whole world will be made forgiven.