rebel, I haven't read that book. However, the statement I'm more familiar with is that most common reason for failure is the lack of a good goal. The good part is important. However, I've not heard it as a purpose. Not that having a purpose in life wouldn't be better than having and achieving good goals.
A good goal, is achievable, within your control, has a measureable success state, has a time limit, and is realistic. I may have forgotten a property or two.
I want to be a billionaire is achievable. It's within my control as much as anything is. I'll know when I get there, provided I can count (or add) that high. I want to do it by tomorrow is time limited, but not it's not realistic. At least not for me. But there could be someone out there that may be about to make it happen.
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As for your life's purpose I've read a few opinions on this. Some say we all have one. However, most don't know it. Some seem to say we all have the same purpose. Few opinions I've seen has said you have to know your purpose. I've seen several that say knowing your purpose is life altering. However, I've seen some say that your life's direction (direction not purpose - semantics maybe) can change throughout your life.
I don't know if you can really know what your or anybodies purpose is. Those that think they do, may only be deluding themselves. If they are happy and not hurting anyone, I say all the best to them.
I'd say that if you don't believe that a purpose exist, then I'd say you won't find yours. I'm not saying one does exist, I'm just saying you won't find one until your beliefs change and you are ready to see one.
I don't think you need one either. However, I do think life is better if you are working in or towards something that you believe in.
I'd say search your feelings and find what makes you happy. If may not give you what you now think of as success, but things will change. Maybe what makes you happy will change, maybe you idea of happiness, maybe your idea of success.
You are perfection.
Iam2 
