Is sticking with your day job a cardinal sin?

If you are attempting to raise funds with an angel investor, they want to see commitment.  It is expected that founders are going to be working full time.  Quitting the day job to work for the start-up is clichéd, because it’s expected, and because it sends a message to the investors.  Also because so many people do it.  The commitment of anyone not working full time for the start-up is questioned.  This may or may not really be the case, but that is the perception.