The game is not showing the Vive hand controllers / gun controllers. What should I do?

Take the following steps when this occurs:

1. Verify that the player is not covering the sensors with their hands.
2. Verify that the hand controllers are turned on and charged.
3. Turn the hand controllers off and back on.
4. If Steps 1 and 2 did not solve the issue, re-sync the hand controllers via the sync function in Steam VR.