What is sin?

I find that, in evangelical circles, sin is often mentioned, but rarely defined.
We are willing to ‘acknowledge that we are sinners’, and the affirm that ‘Jesus died for our sins’, but want quickly to move on to something that feels more positive, more upbeat. Is it that we don’t want to offend (ourselves or others)? Or perhaps that we don’t really feel the ‘exceeding sinfulness of sin’?
Randall Pelton notes a common definition of ‘sin’:
Sin is any lack of conformity to the character of God, whether by act, disposition, or state.
That’s helpful.
But, suggests Pelton, it can be at least as helpful to understand sin in terms of its effects on our humanness.
He cites Hermann Bavinck:
‘It is a deprivation of that which man, in order to be truly human, ought to have; and it is at the same time the introduction of a defect or inadequacy which is not proper to man. (emphasis added).’
‘…sin is not a substance in itself, but that sort of disturbance of all the gifts and energies given to man which makes them work in another direction, not toward God but away from Him. (emphasis added).’
This way of thinking about sin, as Pelton suggests, ways into reflecting on what it means to be fully human, and what it means to have purpose in life – very live questions for many younger people today.