What is the principle of gypsy heart?

The number is a two-digit number, and if it is xy, xy= 10x+y, then the result is 10x+y-(x+y)=9x.

So the result is always a multiple of 9

The "corresponding pattern" of "mind reading" will change every time, so what we see is different every time.

Why is it different that it can guess everything?

A closer look shows that the multiple of 9 in the displayed pattern, that is, the pattern of 918 27 36 45 54 63 728190 is the same. So it must be right.