I'd suggest adding a comma.

FROM:
Of course I understand.
TO:
Of course, I understand.

CK, this sentence is different from #3819010 (which is your own). :)
We had a very long discussion about this sentence, in English, in Russian, in German etc. throughout the past two hours... :)

If you have the patience, you can read the long discussion that ensued (mainly around the same sentence with a comma, and another one without it).

Here it is: #3866416

It was a suggestion. Some people don't put a comma after short introductory phrases.

I doubt if the English really has the difference that you say it does in those comments.
Of course, I could be wrong.

I saw one page that said there was sometimes a difference in meaning, but that page's explanation didn't match yours.

"of course" comma
https://www.google.co.jp/search...rse%22%20comma

The thing is it is the comma which makes the whole difference here. I usually attribute great importance to commas in English (as well as in other languages, but as I work mainly with English on a daily basis, I tried to master the punctuation rules).

Maybe you are right and people don't usually pay attention to a comma in this position. I do.

Of course I know.

It's similar to:
You know I'm right.

You won't put a comma here:
You know, I'm right.

Indeed, you can put a comma there, but then it will have a different meaning (and you will read the sentence with a different intonation).

BTW, I do put a comma here, always (as you suggested).
But in my sentence above, I referred to another sentence, not the one you had in mind. With "Of course, I understand", the meaning is "It's like that, I understand"/"It's true, I understand".

But when there is no comma, "Of course I understand", the meaning is "You bet I understand". I hope I managed to explain it.

BTW 2,
In the examples you specified above, "of course" should be separated from the rest of the sentence by a comma (or two commas, as "delimiters", so to speak). But as I tried to demonstrate above, the expression in the sentence in question has a different function than the usual one of "of course".

Having said that, I would add that maybe, as you said above, there are people who would put a comma here even with the second meaning specified above, i.e., "You bet I understand". I would believe it's wrong.

>people don't usually pay attention to a comma in this position
Hear!
It's a nice distinction to make use of, the comma thing, but I'd strongly oppose making it mandatory as it would forcibly over-complicate the whole picture, and sometimes you don't want it complicated. (Key words mandatory/forcibly.)

Duplicates of this sentence have been deleted:
x #5324929