I have had some sad moments in my 50 years, but none so dreadful as when i found out my banjo was a fake.
I always remind myself that, while these things are valid to be sad about, it can always be worse than it already is.
You mean that it wasn't a banjo after all or that it was not the particular banjo that you'd been led to believe that it was before you acquired it?
You certainly won't get details of people's saddest moment that is too personal a question to ask on a public forum, inappropriate even.
I find the constant, seemingly compulsory exposure of all manner of personal experience on the internet deeply distasteful.