WW I and WW II were both examples- In WW I, each side did ot think the other would react. In WW II, Germany thought that, since there was no action taken re earlier attacks, they were free to take Poland.

If Iran THINKS it can make and use a WMD without being destroyed, it will act on it's past words. Doesn't matter that it will be destroyed- IRAN has to think that it will be hurt, and the present worldview is that it would not be.