The Skill to Convince

I recently notice a skill that I am seriously lacking of.  What is that?  The skill to convince people.  I have a friend who is very easily convinced by sales people from insurance, land banking, and others.  She is the darling of all sales people, as she is so easily convinced into buying all kinds of insurance packages, and even some well-known trouble-some products, yet, I can't convince her to stop buying more insurance policies, as she is already way over insured (although her insurance agent would argue the other contrary). 

That left me wonder why I can't successfully convince people with my ideas.  Is it the skill?  The image I portrayed?  The tone?  My track record?  Or?  I don't know, and that will be one of my tasks to find out why.  The skill to convince is necessary for any successful person.  Great leaders always have the skill to convince.  One good example is Liu Bei.  He is no great master of martial arts, no great strategist, yet he managed to assemble a great team for his establishment. That's something I must learn.