@Jack

I agree with you about conversation scripts. Saying "they are of limited use" is more or less the same thing as saying they are the "very beginning" of building a person's confidence. I general I agree that if you have no experience of practice in class you will find it difficult to communicate, but on the other hand I have taught students (refugees from war-torn countries) who can communicate confidently in English - though they often made many mistakes.

And yes, of course, teachers and teaching materials can simulate real world situations. This is very much at the core of my approach to teaching. Of course it is also true that students must be prepared to take a full part in these simulations if they are to benefit...which bring us to confidence.

 Your definition of the word 'confidence' is accurate, though a little narrow - I would say 'a belief in yourself' is closer to the way I am using the word. But yes, you could argue this is only a feeling, or intuition, and these can be wrong. So yes we broadly agree about this also.

I'm not sure I agree with your example of an airline pilot. Making a mistake with one aspect of language (Grammar, pronunciation, vocabulary) or unlikely to have as bad a consequence as mistakes by airline pilots. I think it is ok to make mistakes, and that in fact we often learn best when we do make mistakes. I believe I do.

Specify the core mission of the learning and punch on it since most people have very limited time.  

@Chris

Confidence this term is actually quite confusing to many English learners, let me tap into the term on dictionary.
"The feeling or belief that one can rely on someone or something; firm trust."

That is sort of feeling, isn't it? A feeling can sometimes lead to you a good place but alternatively it can also guide you to somewhere hopeless through "blind" confidence. A learner with no good manners in learning a language can blindly build up their "false" confidence at home until they really use their learned languages.  

"conversation scripts' are only of limited use.
That is true, but that is very beginning to build up a person's true confidence in a language. A learner with no effective practice in a class (or in private) is impossible to build up their "true" confidence.  I agree with Sudeep that all elements in a language (grammar, vocabulary, phrase...etc) are all important to become a proficient speaker.  

"When they don't follow the script?"
Therefore, teachers, or teaching materials must well  "simulate"  real situations or scenarios for learners in order these learners to use the language in a "real" world fluently through building up their "true" confidence just like training a pilot to steer a jumbo through a useful and practical simulator.   

Will you place a rookie to an airplane as a pilot with little experience on simulators? 

Thanks Sudeep and Diana. I think you're both right that we need all of the elements. Especially for Beginners.

I guess I'm thinking mostly about conversation once people get to Intermediate (B1) level and upwards. 

Sudeep - your analogy about making your favourite dish is interesting and valid, but I have 2 additional thoughts about this. 

The chances are you made it before or you will have at least seen it and tasted it (otherwise it could not be your favourite) - therefore we need to also add 'experience' to the ingredients that are required. Which is why all the practice listening, speaking, reading, writing tasks are important when learning a language. But learning 'conversation scripts' are only of limited use. What happens when you need to make something 'new'? Or when the other person you are communicating with wants a different end product? When they don't follow the script? This is when I would argue that confidence is most important.