What is the essence of the Haeckel-Mueller biogenetic law?

Haeckel-Müller biogenetic law states:
Each individual in individual development (ontogenesis) repeats the history of the development of his species (phylogenesis), or, ontogenesis is a brief repetition of phylogenesis.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.