The Secret has a lot of things going for it. It emphasizes the importance of thinking positively and acting with confidence. It encourages people to affirm the abundance in their lives and to be grateful for what they already have. All of those are good things. If we think negatively and feel depressed, we're not likely to have amazing outcomes.
On the other hand, there are times when people work as hard as they possibly can but encounter numerous obstacles. If they don't succeed because they struggle against systemic racism, poverty, discrimination or debilitating illness, it's not their fault and there's no way that they can talk themselves out of that situation. They might be able to deal with it better but I preferred the more rational thoughts of Norman Vincent Peale to The Secret because he never blamed anyone and he was always sane and rational about who could and who couldn't further themselves.
There's a reason that the serenity prayer became very popular in 12 step programs and that's because there really are some things that we CAN control and other things that we CAN'T. Rape, child abuse, sudden dismissal from a job, a spouse dying, working at a crappy job for minimum wage... those things are out of many people's control. When we get into Third World issues, applying The Secret becomes ludicrous. Can we feed Ethiopians, eradicate HIV, boost sagging economies that are strangulated with debt? Hardly. No matter how much someone with AIDS in Kenya affirms that he is healthy, he won't be!
Don't get me wrong. I own The Secret and have watched it several times. For middle-class folks who are reasonably healthy, it's possible that the techniques here can make them happier and more successful. Having an attitude of expectancy is always a good thing unless we blame ourselves when our dreams don't materialize and we never had a chance in the first place.