agree with your opinion, put all of our money in bitcoin is something wrong, we must ready for any case, we must save our money at fiat too, or maybe in gold or property.
If I personally had to choose two investment options, then one of them will be Bitcoin for obvious reasons, and the other one would be Gold.
Mainly because of the fact that real estate prices are too damn high at this point. I never buy myself into a bubble.
And it's never a bad idea to only have a single investment if people are really getting decent profit out of that investment.
In real world, there are succesful businessman who really touches the stage of being a rich one even with only sole investment and business.