לע"נ הרב משה בן הרב מנחם ז"ל
רבקה רחל בת ר' מרדכי ז"ל
ר' אליהו שמואל בן ר' יוסף זאב ז"ל
עטל בת ר' שלמה אריה הלוי
ולזכות נכדם ידיד נפשי האהוב הרב הגאון ר' זאב שליט"א וכל בני ביתו!
Someone had a hot water boiler [called in Hebrew a "דוד" - or "dude"!] that wasn't working and he called a fix it man to install a new one. The man arrived and fixed the "dude" of a fellow from a different apartment [what a dude!!]. The installation was not immediately helpful but will be helpful in the future [because now he has a brand new dude so it will take much longer for anything to go wrong]. What is the din?
Apparently the person who benefited must pay for the benefit of a future fixing. The din is that a יורד לתוך שדה חברו שלא ברשות ונטעו - If one enters his friend's field without permission and plants it the owner must pay. That would be the case here. He benefited the neighbor who must pay.
But one can argue [which Jews like to do] that this isn't so because he completely exchanged the dude which makes him not a יורד לתוך שדה חברו but a goneff!
However since the worker didn't know maybe he has a din of a גונב באונס who is exempt from payment and therefore his status is now as a יורד. This could be compared to a case of someone who stepped on his friend's object on the street [where he is exempt] and now he fixes it. In such a case it is simple that he has a din of a יורד [even if he never left Israel. Get it - "יורד"].
But hold your horses - if someone accidentally hit his friend and is exempt because it was 100 completely not his fault [called in Batei Medrash worldwide "אונס"] and then drove him to the hospital - would he be considered a יורד and the victim would now have to pay for the ride??? So how can we say that after someone causes damage we permit him to benefit from the damage he caused?!
[מאוצרות הגר"א גנחובסקי זצ"ל]