The theory is that it is good to know where you have been so that you can work out where you are going. Generally, this is used when referring to nations, but it is applicable to families, and even individuals. To me, it means that it is a good idea to learn from and build upon what has gone before. This is a different kettle of fish to the other maxim that is bandied about: ‘those who forget the past are condemned to repeat it’. However, upon reflection one could be the obverse of the other – the positive, followed by the negative.
Families are dynamic entities to ponder, dynamic meaning fluid and ever-changing. It is salutary to compare the pathways taken by the families of siblings, and to trace the impact of differing personality traits as they bind or divide, traits like openness, conviviality, and a certain meanness of spirit.