I'll give you an example.

Say you have 3 TH/s and you're burning 2000 W per hour. That's 2 KWh, or 48 KW per day.

At $0.10 per KWH, that's 4.80 a day.

3 TH/s at current difficulty is $8.58 per day, according to bitcoinwisdom. At current price of $240ish. However, the price was not always that....

So, your profit is $3.79 per day, you would think. But you would be wrong.

Your miners cost something, be it BTC or fiat. So, at current difficulty, and with difficulty adjustments, how long will your miners be profitable??

Will you sell your BTC now, or later, and take a chance on prices going up??

Do you have bills to pay? car payment? eating? That electricity bill can be a little pricey, as can the miners.

All that comes out of that alleged profit. There are LOTS upon LOTS of considerations.