With no doubt, experience is the best teacher which teaches individuals how to treat or make a decision in the future.
There is nothing wrong with this sentence in terms of grammar or vocabulary. However, it is good that you start with introducing the topic. Since this is an agrgumentive essay you need to show the other side of the argument also. Once you introduce the topic, you can state your opinion as you did above.
For example, scientists who investigate natural phenomena are convinced that they can make a better conclusion when they get experience during their research and are able to cope with obstacles.
I doubt whether this is a good example... Scientists have gained lots of theoratical knowledge before getting on to research. Without that they would not be able to carry out research. However, you can use a different example such as a car mechanic... He's a guy who works with more " know how" than book lessons. Always pick more specific and relevant examples to support your reasons.