The better you know them and more you can set boundaries, the less that person can hide behind the excuse of the illness and face reality. Of course brain chemical imbalance makes it harder for some than others, but ultimately believing we have power over our lives leads to more responsibility and peace, regardless of the underlying biological situation. But it never is easy to know are they being "mad" or "bad", and it is best we only do what we are prepared to, to minimise our resentment.