text=In order to understand this phrase, you have to know something about the history of the Israeli Bezek phone service which is also known fondly as the Nezek (damage) phone service. Until recently, there were no such things as phone cards or special credit numbers, etc. If you wanted to make a call from a public telephone, you would have to buy these small tokens with a hole in them, known as asimonim (pl). In the days of hyper (350%) inflation, people used to hoard them as a hedge against inflation - no joke.
In order to make a call from a public phone, you would pick up the receiver while holding a bunch of asimonim in your other hand, put one in, and wait. Here the key word was, wait - for a dial tone. Then dial and wait again until finally you were connected to your party.
At this point, you had to both talk and keep feeding the tokens into the slot as fast as you could. Otherwise you would be disconnected and have to do it all over again. So “Nafal HaAsimon” is used when something finally dawns on someone, when it clicks, when things finally connect. As you see the recognition in his/her face, you can say “AHHH, Nafal HaAsimon.” Somehow “Nafal Ha bezekcard” just doesn’t cut it.