mentch, often having a “nes” is a last-resort action to protect someone and may take away your zechuyot. To use your analogy, you will be better off using air defence to protect your home than relying on the nes to have debris falling around you. In Taanis 20, R Huna is using zechuoyos of another Chacham to save wine from a shaky building and the chacham is not happy about that.
