when I watched youtube, I got the new information. 'sure' isn't similar to 'of course'.

OMG... I totally didn't know that.

Its definitions are like below

1. The response you give when you don't 100% want to say yes but also don't want to say no. Sure is the answer you use when on the fence about something. It's not an acceptable response to yes or no question.

2. A comment/statment made when an individual would like to imply sarcasm or a lack of interest toward somthing someone else says. Sure can be pronounce in a very high pitched manner and maybe accompanied by sarcastic head nodding.

3. Often used sarcastically, it origianally means "I agree".

When said quickly, it stays true to the origianal meaning.

When elongated, it is often an indiction of sarcasm.

4. 'Sure, sure, sure' means 'I don't wanna hear any more.'

I used 'sure' many times in response to my Korean-American friends. And sometimes they seemed to have difficulty about asking me for help. Besides, when I asked them for help, I heard only 'of course' in their answer.

If they ask me for help again, I'll answer 'of course' instead of 'sure'.