Circuit Confusion with Ground
In the first diagram, your hand is touching a high voltage and your foot is touching ground. There is a large potential difference across your body. This will cause a current flow through you, which is what you don't want.

In the second diagram, your hand is touching ground and your foot is touching ground. There is very little potential difference across your body. Since there's no potential difference across your body, no current will flow through you, and you won't feel a shock.

If you touched both your hand and your foot to the high voltage wire (like birds sitting on a power line) you would also have very little potential difference across your body and not be shocked. But you'd have to find a way to get to that position without starting in the first position. Perhaps learn to fly before you try this experimentally.