How many times have you flown, in your life? And how many times have you heard the flight crew explain the safety instructions, the oxygen mask and the life jackets and the flotation cushions and all the rest? If there were really an emergency, would you know what to do? Yeah, me neither. We don't really pay attention to instructions until we need them.
A key problem in all user interfaces...
This is why affordability is so crucial. People have to be able to figure out what things are for and how they work "on the fly". I'm guessing I would be able to use an oxygen mask, or inflate a life jacket, or use a flotation cushion without instructions, because of their inherent affordability.
Would my customers be able to use my software without instructions? I'm guessing yes :)