Sin is allowing evil to influence your karma.
Evil thoughts can be controlled, but to sin is to let these thoughts influence your karma.
To gain pleasure temporary, and suffer afterwards, and keep doing that while knowing its wrong.
Sin is always linked to desire.
Without desire there would be no sin.
Without desire there would be no suffering.
The seven deadly sins are greed.
Because you have to always watch your back and people, distrusting honest folk perhaps (Suffering)
And you do all in your might to gain that extra loot, even go as far as to steal and lie. (Sin)
Lust,
Because you always desire that feeling once more, yet it shall always dissapoint unless you forget it. (Suffering)
You'll hurt others perhaps and lie and cheat, but that loving feeling you will never get (Sin)
Envy,
The mind is roaming with the things you desire, and you see others that have it wish they had not (Suffering)
You break their possessions or steal it and keep it, your mind is material and no longer with God (Sin)
Sloth,
You do your things, but you do not want to. You keep telling yourself i don't want this (Suffering)
You avoid responsibilities in order to do what you like, and troubles will pile up to your throat (Sin)
Wrath,
You wish harm upon others, but you only hurt yourself. You drink poison and wish others would die (Suffering)
You cause harm to others, and wish to harm once again, for you hate and hate and hate and you sin (Sin)
Pride,
You carry pride, and feel better than other's, you act like the devil and thus it shall target you (Suffering)
The ego is strong and you no longer share, enjoying is no longer a thing you can do.