I wonder why JJG cares so much about others money. I've seen over 15 posts by JJG saying that mining will be not profitable. Of course in a long term there will be only miners who have electricity for free. But for now, difficulty adjusts to current price so mining is almost always profitable.
You're missing the point.
I'm not talking about mining, I'm talking about running out to buy dedicated mining hardware with the belief that it will just pay for itself in a few months and then continue generating income for the owner indefinitely.
My registration and posts were prompted by some posts on this forum and a few others. In one example, someone spent $3000 on a dedicated mining rig and expected to pay $151/month in electricity, but hadn't bothered to take difficulty increases into account. By the time he received his hardware arrive, difficulty was up 19%. In ~9 more days, it jumps 30% (if not more). That means only a week or so after he started, his profits were already only 2/3 of what he predicted he'd make. If another 30% difficulty increase happens after the next one, his profits will be 1/2 of what he predicted.
A lot of the miners who come to this forum are starry-eyed with profits they roughly calculated, and eager to buy all the mining hardware they can. After all, it's free money, right? Well, realize that it's a race to the bottom and you're up against a rapidly increasing difficulty value that is
explicitly designed to keep you from making easy money indefinitely. That's the system, and that's how it works.
Meanwhile, the influx of miners generally aren't intent on actually using bitcoin, they just want to do some mining and then immediately cash out to pay off their hardware. When scores of miners are desperately trying to sell their BTC to pay off their hardware investments, the value of BTC is going to fluctuate wildy, and the general direction won't be up.
Plenty of people have run the numbers. Curve fitting the rising difficulty is a trivial task, more advanced models don't tell better stories either. But none of this stops the "I want to believe" crowd who thinks that they're going to turn 6990s into indefinite cash streams.