When we are being perfectionists, we are acting with total faith in the self, total faith that with enough effort and training, we can make the self into exactly what we think it should be. We think we can make it function exactly how it 'should' function.
Of course, the Buddha's discovery was that this self that we have so much faith in does not exist. There is no "absolute essence of me" that can be made perfect. The self arises in the field of perception in the same way a mirage does. Certain conditions cause our brain to perceive something that is not actually there. All we are, all the self is, is an expression of conditions.
When we think, "I should have been better than that," or "I should have been more of a Buddha," when thinking about how we got angry when that person cut us off, we are in the thrall of a narcissistic delusion, that we are so special we should not react the same way an ordinary person does to a situation.
The Buddha's discovery was not a hopeless one. What the Buddha discovered gave him the freedom not to be a slave to conditions, gave him the freedom to imagine and make different responses, the same as Jesus (William Blake described Jesus as an avatar of Imagination): if someone harms us, we can forgive and wish them well instead of lash out and harm them in return.
But this ability to act differently doesn't come out of guilt or self-punishment. It doesn't come out of worship of the self. It comes out of dropping worship of the self. The same act (dropping the self) that allows us to accept and forgive ourselves for being angry causes the anger to fade more quickly, because who or what are we defending? It's not that we force ourselves to "be better than that" and not flip someone off and tell them to fuck their mother, it's that when the desire to do so arises, it feels absurd, and we don't do it because we don't want to. And when we do want to, we admit it to ourselves, and accept the consequences if we choose to do it.
Waking up is not about making myself into a saint. It is about seeing what is actually going on. When I see what is actually going on, the desire to do a lot of stupid shit falls away. Not all the time, because some days I am too addled by the heat, too exhausted, too psychologically wounded to see clearly or act from a place of equipoise. And I can see and accept that, because I no longer believe in the Gilded Self, the transcendent entity that is Me and that is Better than Others. Like all other beings, I find myself caught at a nexus of various conditions. These do not have to dictate my response, but they will inform it, because I cannot remove my self from those conditions. Take those conditions away, and that self goes away too. Because my self is not some solid, unchanging entity that is independent of circumstances. It is instead, the expression of circumstances.
How is it then that we can ever act creatively, rather than simply react instinctively? It is because there is a part of us that can override instinct--what Blake called our Imagination. But this part of ourselves is not the self, it is not a self at all. It is not a transcendent 'True Self.' It is just the Tao, just the way things are when stripped of the illusion of a self. Our ability to look at, respond to, and act in a set of circumstances not from the perspective of a self, but from a perspective of the situation as a whole. When we see how all the different players and parts of a situation act as a whole, we are free to act based on how we think we can make the best result overall, rather than how we think we can make the best result for Me. This frees us to see how giving up the best spot for ourselves might make someone else happier than holding on to the best spot would have made us. It frees us to see how a peaceful or harmonious result could play out overall if we don't defend and attack from the perspective of self. And sometimes, it frees us to see that taking care of ourselves is what needs to be done, because just as we are not unnecessarily defending the self, nor are we unnecessarily attacking it either.
We are not "spirits in a material world." We are not Selves that can become ever more Perfect. We are mammals, mortals, in a violent and constantly changing world. Our saving grace is not a transcendent soul, but imagination. We can imagine, and act, and make a different world. But we can't escape it or rise above it, we can't become breathatarians or catch a ride to Alpha Centauri. As Buddhists, we have freedom from the wretched delusion of sainthood, which has led so many people of noble sentiments to do such atrocious things, thinking themselves appointed by God to do them. No, we are free to be our perfectly imperfect selves, knowing that the self is no more a thing of substance than a rainbow.