It is a subjective tendency to throw every care to the wind by not protecting the mind from the emotions and evils which accrue through them.What is unconcern? It is to preserve in passion-lust, aversion-hatred, and bewilderment-erring aggravated by laziness. It is not to attend to what is positive and so also is not to protect the mind from those things which cannot provide lasting satisfaction. It provides a basis for increasing the unhealthy state and decreasing healthy ones.-Abhidharmasamuccaya
The Pancaskandhaprakarana states,
What is unconcern? It is not to attend to what is positive and not to protect the mind against the emotions through either passion-lust, aversion-hatred, bewilderment-erring, or laziness.Its function is easily understood.