Just because the future is uncertain doesn't mean you can't do research to make a reasonable forecast. Typically speculation is specifically buying/selling without any reasoning other than 'I think someone will pay higher for this in the future'.
Many assets don't even have to appreciate. A car is an asset if I have paid it off. I don't expect someone to pay me more than I paid for it unless it is a collectible or I live in the year 2021.
On your last sentence, I don't know who thought real estate was 100%, because nothing is 100% safe as a store of value, but I guess they paid for it in the end.