Draw a line with your finger and let your alter ego finish first!

When you write a line, your alter ego runs over the line.
If you release your finger, the line stops there.
If you start drawing the line again, the previously drawn line disappears and your alter ego, which was running on it, falls into the sea and you have to restart from the starting point.

It's up to you whether you want to draw the line on a slightly risky but faster route to the finish line, or on a slightly more circuitous but safer route!