Your argument is Valid, but not Sound!

Watching a lecture on critical thinking, I learned there is a big difference between a valid argument and sound argument. I had heard these words many times, I could sense the differences, but I had never formally learned them.

Can you believe that this argument is valid?

"I live in Trieste, and Trieste is in Iran, therefore I live in Iran";

First, we should learn what a valid argument means: in a valid argument, if you assume that the premises are true, then it is impossible (under no conditions) that the conclusion could be false. For instance, in the above sentence, if we assume that supporting reasons are true, that I live in Trieste and that Trieste is in Iran, then there is no other way that I do not live in Iran. However, what about this:

"I live in Italy, and Trieste is in Italy, therefore I live in Trieste".

It is invalid, because if we assume that the supporting reasons are true, the conclusion can be false because I might live in Rome, not necessarily in Trieste.

What about a sound arguments? A sound argument is stronger than a valid argument. If an argument is valid and its premises (supporting reasons) are true, then the argument is sound. For instance, the first sentence:

"I live in Trieste, and Trieste is in Iran, therefore I live in Iran";

though it is valid, it is not sound, because the second premise "Trieste is in Iran" unfortunately is not true (missing my family in these Christmas holidays a lot :( ).