Quoted from Reality_Studio:

Ok I'm guessing you don't get it, so I'll explain with a real world example step by step:
1) I pay my credit card in full each month, hence the cc costs me $0. It's free.
2) We had to get two next day plane tickets to Canada last December due to a medical emergency, those plane tickets being next day had a price tag of $4200.
3) If I never used a credit card I would be out $4200 today. Instead I used air miles that I got from my credit card, hence I did not spend $4200.
If I didn't have my cc and instead used cash or debit card, I would be out $4200 right now. Because I used my $0 cc, I took that $4200 and used it instead to buy AC/DC Luci. Result? Credit card was 100% pure profit.
That is but one example. I could go on and list more yearly savings and profit, like how we stay at the Cosmopolitain hotel in Vegas free every year from using hotel points from my $0 free cc, but I think you get the point. Side bonus, this free cc money is tax free!
Does that make it more clear? Or does piles of free money each year still seem stupid to you? I don't want to sound curt and abrupt, but it's really win-win assuming you pay your cc in full each month. It's quite literally piles of tax free money and all you have to do is pay your card each month.