Taking a course does not make you an expert. You become an expert by investing enough time, energy and sweat to really learn something in depth. How much time? Malcom Gladwell, in his book Outliers, popularized the 10,000 hour rule;
“The idea that it takes approximately 10,000 hours of deliberate practice to master a skill.” (Read more about the 10,000 hour rule.)
A good course is like a map. It can show you the route, but you still have to travel it yourself.