What is the difference between I stick to my plan and I am sticking to my plan
When I was watching an English movie with English subtitle, I noticed a sentence like
a.Sam asked the hero," did you change your plan.?"
b.The hero said, "I stick to my plan".
This is the context.

My question is why present simple used here "I stick to my plan", not present continuous "I am sticking to my plan" used here?

Question

What is the difference between I stick to my plan and I am sticking to my plan
When I was watching an English movie with English subtitle, I noticed a sentence like 
a.Sam asked the hero," did you change your plan.?" 
b.The hero said, "I stick to my plan".
This is the context.

My question is why present simple used here "I stick to my plan", not present continuous "I am sticking to my plan" used here?

Answer

I agree with Joshua.
I would say that "I stick to my plan" sounds more like a final decision the the hero won´t change.
The sentence "I am sticking to my plan" would be more like saying that the person has the intention to follow the plan but the situation might change if something happens

Answer

"I stick to my plan" sounds like a statement. Sounds like the hero wants the listener to know that the plan is a commitment.

Answer

Which movie?  Is there any more context?

Answer

Thank you sir.

Answer

The response does not really fit or make sense.  It should either be in the simple past tense (stuck) or else he should have used the present tense to refer to something which is generally true , in which case plan should have been pluralised, i.e.

"I stick to my plans," with the implied meaning being that the speaker never changes his plans and that, therefore, the same was true in this case.