There is no investment worthing ok? I don't agree with all other investments said here like casino, alt coins, mining and all other. All of these investments will give you low return or aren't safe enough to give you stability. Just hold your btcs and use it as money to buy stuff.
Investment with btcs don't work, people on the internet are only looking for your money (to steal it). Any moment this can happen, be prepared!
I am definitely agreeing with you that
there is no better investment than simply holding your coins safely offline. But the point is that a lot people here want to put their coins to work in the way that they will increase in quantity. Exactly this is what makes people put themselves into big risks. Especially because of the fact that most of the investment options are either a scam from the start, or they will become one at a later stage when their site or service doesn't bring in a decent amount of profit anymore. That's why every investment option must be treated as such at the very beginning.
This is debatable on strictly objective statistical grounds. It is not given that Bitcoin will grow in the future and won't collapse to lower hundreds at the end of the day. So just keeping bitcoins offline doesn't make the Bitcoin investment free of risk altogether. On the other hand, the growth of Bitcoin is never linear. I mean that today's price is not always higher than or equal to yesterday's. Corrections do happen, and the higher the price rises, the deeper and thicker they will become...
In this way, the least risk mode of investing in Bitcoin would certainly not be dumb holding but holding with a little bit of selling and buying now and then