When you find out someone you've known (acquaintance, coworker, family, friend, etc.) has a mental illness, how do you react/respond?

If you’ve known someone who has seemed healthy, without any symptoms of mental illness, and this person has disclosed to you he or she has a mental illness (depression, bipolar, schizophrenia, personality disorder, ADHD, etc.), how did you react/respond? Were you open and supportive? Fearful? Did you want to discontinue contact, but have chosen to stay in the person’s life?

Also, what are your attitudes and beliefs about people with mental illness? Literally, what do you think and how do you feel about such people? About mental illness itself?