The third house is of confidence and your inner stamina and the sixth house is of your fears. And we know that any planet in the tenth house from its house makes or strengthens its house, so the sixth house is naturally strong. Now when the 6th House Lord In 3rd House then the native may suffer from inner fears. The native does not have that much strength internally. The native lacks confidence. The sixth house being strong in the third house brings a lack of confidence in the native. The sixth house is of logic and the third is of communication, so the 6th Lord In 3rd House in the third house is very logical in communication. The person always has a logic for every action.