Pianos do not naturally go out of tune this badly! For a single note on a piano to be this wild, it is highly likely that a previous owner tampered with the tuning pins in some way, perhaps in a less-than-successful tuning attempt. It would not be the first time I’ve run across that…
I don’t ever discourage people from working on their own piano – in fact, I think it’s a good thing. Just make sure you do your research first and know what you’re getting in to! Suffice it to say it’s more complicated than it appears.
