Any actions motivated by greed or attachment are what we could call sinful actions, where the meaning of sin is simply to forget who we are. When we forget who we are i.e. eternal souls, our actions arise from a false belief of who we are and those actions are therefore inaccurate and negative, often destructive. Our capacity to be loving, peaceful and contented is reduced. Although we grow used to tension, dissatisfaction and being upset, we don’t realize that these emotions have their roots in forgetfulness of the true self. Over time, the record of all thoughts and actions, which are driven by these negative inner states, accumulates within our consciousness and heaviness sets in.
Negative action is also a result of misuse or abuse of one or another aspect in our life: of the body, of relationships, of wealth, of our thoughts, etc. Taken on a simple level, if we keep eating lots of ice cream and do no physical exercise, it is certain that we will gain weight at some point in our life. Our bodies are not designed to take in more calories than they burn, producing a negative result. We are able to see the results of our actions on a physical level, but it is not so easy to see the negative results of our actions on a mental and emotional level.
Neutral actions (akarmas) involve routine tasks which do not normally negatively affect others: working in the office, cooking food, going to the market for shopping, etc. However, even those actions, if carried out in a state of body-consciousness, can easily become negative on a subtle level and a further debt or heaviness may be accumulated.