Outside and barefoot your body provides an easy way for the current to reach ground.
Work Step by Step
If you are outside with bare feet, and an appliance malfunction exposes your hand to a voltage, the current has a direct path to the Earth through your body and feet. You will receive a strong shock. On the other hand, if you are inside wearing shoes with thick (insulating) soles and the appliance malfunctions, the current won’t have an easy path to ground through your body. Any shock you receive will be milder than in the first case.