Sin is firstly ‘original’, meaning that it is something we are born with. Christians believe that wrongdoing is more than mere ignorance of how we should behave, it is deliberate defiance, choosing to be selfish or worse, despite what we know to be good. This is born in us and needs to be overcome. The Genesis Garden of Eden myth makes this clear, as Adam and Eve wilfully eat the forbidden fruit and suffer the consequences.
Secondly, sin is a struggle. St Paul speaks of how all have sinned and fall short of God’s standards, that it is as if there is a law pushing us to go the wrong way even when we know the right thing to do. In Christian teaching it is the grace of God that helps us to overcome this tendency, along with self-control and the guidance of scripture and conscience. This is in stark contrast to the fact we are made in God’s image, but just shows the power of free will.
Thirdly, sin is structural. The rich are constantly told to ‘ease the yoke’ of the poor in scripture and not to oppress them; Jesus complained of the burdens the Pharisees placed on ordinary people, and we can see in the world today that global capitalism can have a corrupting effect on whole societies in the pursuit of greed over against the welfare of those in developing countries and the environment. Such sin traps the weak in systems that damage their lives through poverty and oppression, and can lead to violence and other desperate acts to bring about change.
Finally, sin is of this world but not of the next. St Paul makes it clear in his letters that Jesus has "paid the price for sin" and the book of revelation describes heaven as a place of no sin where people will no longer go wrong. So it is that Christians believe they must keep focused on the kingdom of God and try to be as they will be in that eventual state.