Ok, visualize it like this:

Draw yourself, with a small mirror at head height, a meter away. Draw your reflection at the same distance from the mirror on the other side.

Now do that again, but place the mirror 10 times further. Then draw lines from your eye, to the edge of the mirror, and to the reflection.

You’ll reach the same point on your reflection.

Edit: or let the BBC do it for you; https://www.bbc.co.uk/bang/images/dallas_mirror_diagram_large.gif