Clearly, the fact that Otto Frank was the only member of his family to survive the Holocaust and the war suggests something about his strength of character and will. Otto Frank worked in Frankfurt as a businessman, and achieved great success. He is the architect of their removal and hiding and the way that they were able to remain undiscovered for so long indicates how clever, intelligent and canny he was. Also, he was a very good reader of persons, choosing very carefully the right kind of people to take into his confidence who would help him and his family.
Although Otto Frank's plan ended in failure it is important not to underestimate what he actually achieved: for more than two years he succeeded in protecting his family whilst also continuing to have a role in running his own business. This speaks volumes about his strength and foresight. His role as unofficial tutor to the three children also indicates his intelligence. In the face of danger, perhaps because of his own military experience, he responds rationally and calmly, not with fear or terror. Perhaps it is this ability that allows him to survive the horrors of the concentration camps.