Suppose you think that 3+4=6.

I offer you the following deal: give me $3 today and $4 tomorrow, and I will give you a 50 cent profit the day after tomorrow, by returning to you $6.50. You can take as much advantage of this as you want. In fact, if you like, you can give me $3 this second, $4 in one second, and in the following second I will give you back all your money plus 50 cents profit - that is, I will give you $6.50 in two seconds.

Since you think that 3+4=6, you will jump at this amazing deal.