To measure success, you can quantify your expectations and when you exceed expectations you are successful.
Success isn't an unambiguous result. It needs to be seen in a clearly understood context.
Shawn, in such things, perhaps taking an opposite perspective allows for the deepest more valuable kind of perspective... according to Winston Churchill,
'True success is the innate ability to move from one failure to the next with undiminished enthusiasm.''
It is much in the vein as Mark Twain who maintained, 'We are all ignorant, only about different things.''
Success can be defined in many ways, Shawn. As a coach and marketing professional, I feel if someone loves what they do, they are successful. Success to me also means time to enjoy life. Years ago when I was on the metro midday, (actually en route to pick up my car from being serviced) a woman asked me why I wasn't "at work", and I said I was self-employed. She said, "You must be very successful then." When I asked why, she replied, "Success is being free." I've never forgotten that definition, and still think it's a great one.
I try to establish metrics to everything that I consider significant. If the metrics are met and the intended results occur then I consider it a success. If I fail to reach my metrics but learn some vital information that will help immediately or in the future I consider that a growing pain. : )