Use of "do" in affirmative statements [duplicate]
Solution 1:
Well, since
I do think apples are good.
and
I think apples are good.
mean the same thing.
I think it's just for emphasis.
Solution 2:
Could be used in either of these two situations, with quite different nuances:
Refuting a claim: "You're lazy! You don't work hard enough."..."What? I DO work hard!".
Admitting the truth of a statement: "You should work less or you'll have a heart attack."..."Maybe you're right, I DO work hard."