My experience with mental illness has made me more understanding -- but not necessarily tolerant -- of others who are late, who cancel plans, etc. when I know or suspect they may have depression.

Also, I did not understand many symptoms abuse survivors show (for example, apologizing constantly for things they don't need to apologize for) and even was intolerant of the behavior of a former roommate who I now know was a victim of abuse. (I feel very guilty for this.) Now that I have suffered abuse myself I understand and am empathetic.