What makes a good language learner?

Sometimes I see the advertisements in the newspapers and on the buses claiming that it is easy to learn English. According to these advertisements, with very little effort on the student’s part, he will be able to speak the language fluently in three months or even ten days. When I see advertisements like this I don’t know whether to laugh or cry. If it were as easy to learn English as they say, I would have to look for another profession, because very few qualified teachers would be needed. But a large number of people must believe these ridiculous claims, or the advertisements would not appear.