In fact, you don't know their full name, whether you will ever see them again and have only a tiny clue to who and where they might be.
Back in September of this year, holidaymaker Liam Muns, 34, who was in Disneyland Paris, suffered a major health scare after choking on his food at a restaurant one evening.
A first aider was needed and thankfully sitting just a few tables away from Liam and his family was Harry Patrick, a volunteer with Mullion coastguard rescue team, who was on holiday too, with his family.
Earlier this year - in June, Harry acquired new-found first-aid and life-support training skills as part of his operator role with HM Coastguard, and he was able to put that knowledge to use there and then, in the heat of the moment.
Indeed, his intervention - alongside one other person who offered immediate assistance - proved to be life-saving.
Not only was Harry able to perform the Heimlich manoeuvre, he was also able to co-ordinate an ambulance to arrive at the restaurant, despite a language barrier and the obvious commotion involved during a busy time for the venue.
As Liam was moved into the ambulance, the two men exchanged a few words, in which Harry mentioned he was a HM Coastguard volunteer, based in Cornwall but owing to a mix-up, telephone numbers weren't properly exchanged.
Liam spent four hours at the hospital - an anxious wait for his family - but was then able to leave relatively fit and well.
Back in the UK, and determined to track his life-saver down, he sent out a speculative Facebook message, directed to the Falmouth coastguard rescue team page, in the hope of finding the man who helped save his life and to say thank you. And, fortunately, with the help of Martin Leslie, a coastal operations area commander in Falmouth, and the Maritime & Coastguard Agency, it was possible to put the two of them in touch.
