Normally, first base isn’t stolen since you have to hit a ball to get on a base. To steal first, Germany Shaefer had to go back to first base from second base. It wouldn’t seem to make sense at all to go backwards in a baseball game, which is why Germany is the only one who has ever done it.
Germany’s decision to go back to first base was strategic, even though it must have looked like madness to those watching him play. A common play at the time was to have a player on first steal second, in order to distract the pitcher from tagging out a player on third base trying to steal home plate. Germany ran back to retry that play, which had failed the first time he used it. It succeeded.
Germany tried the same tactic in another games against the Chicago White Sox. The manager of the White Sox came out to complain. In 1920, a rule was passed which called a player out any time they tried to go backwards on bases after they had legally gotten another base. This meant that Germany would be and will be the only man ever successful at stealing first base.