Quora Isaac Wilkowski:
Mining is a speculative endeavor. You are banking on an investment making returns. You use current and expected future prices to determine an expected gross value and you use mining difficulty and likely of successfully mining a block to determine expected costs. Together these provide expected profit, if you're interested in mining look at calculators for this.
The problem is that all of these variables change and are related. If price goes up, more people mine, and the mining difficulty goes up and you are less likely to be the person who wins the block. That means that if people want to win, they need to mine smarter. So they don't use cpus, they use gpus and Asics. These are more powerful than cpus per dollar and therefore win on average. For bitcoin or litecoin, you're not going to make money without multiple Asics. For ethereum and everything else that doesn't have asics, you're not going to make money without multiple gpus. And even if you do everything right, you may never make enough to recoup your investment on hardware.
So if you want to mine with a CPU you need to mine something nobody else thinks is worth mining, and be right. Which you probably won't be.
You would be better off investing your money that you would spend on power and electricity in currency you believe will go up in value
