The concept of repentance is a difficult one for even Christians to grasp, I think; and non-Christians seem to be baffled by it altogether.
Yet repentance is, if not at the core, then very near the centre of Christianity; because it is repentance which is required for salvation - and not virtuous behaviour nor sinlessness (which are regarded as impossibilities).
One way to think of repentance is as a kind of learning - and indeed, the set-up and purpose of human mortal life can be understood as being about learning.
Since humans are so weak and prone to err and sin; and the world is so full of temptations and suffering (as well as beauties and joys) - then it seems clear that we are not so much meant to behave perfectly as to learn from our experiences - and perhaps especially from our errors.
We learn by acknowledging our errors; indeed (thanks to the work of Jesus Christ) that is all that we need to do for salvation - but we do need to do it. We do need to acknowledge our errors.
The usual way of saying this, is that we need to repent our sins. Sin is another concept which modern people cannot grasp - and one way to think of sin is as errors... but errors that must be recognised as errors.
Thus sins may be errors resulting from various causes - such as doing what comes spontaneously, yielding to pressures, done from ignorance, done from wicked motivations, or by being too short-termist or selfish in choices or behaviour... but the vital thing is that after they have happened, they need to be seen as errors.
This means that errors must not be self-excused, nor denied.
Denial of errors is perhaps the commonest and most dangerous of modern problems - instead of acknowledging that X was an error, the modern tendency is to deny that it was an error - then, because neutrality is impossible, this denial rapidly slides-into asserting that the error was an intentional virtue.
Perhaps because errors are understandable - or because we could ourselves imagine doing them under certain circumstances - or because they seem excusable given an individual's situation... the inference is made that 'therefore' they are not errors at all!
From this, we get the situation in which errors are taught - and errors are taught to be superior modes of behaviour. Errors are taught, laws and rules are implemented to protect, promote and reward deliberate error. People are taught to have pride in error. (And conversely, virtue is punished.)
This situation is extremely dangerous - indeed it is hard to imagine a greater spiritual danger than one in which errors are denied and/ or asserted to be superior to virtue.
The solution is necessary, swift, simple and unstoppable: it is repentance. But repentance becomes impossible where errors are regarded as higher truths. And that is precisely our situation in The West.
So me must re-learn to acknowledge errors, and to repent them. It sounds simple - but from where we are, here-and-now, the prospect seems horribly remote.