Most people think of haircare as something that happens to the hair itself. The right shampoo for shine, the right serum for frizz, the right oil for growth. These things have their place, but they're all working on the hair shaft, not on the environment it grows from.
The scalp is the soil in which every strand of hair is rooted. And just like plants grown in poor soil tend to be weaker, thinner, and less resilient, hair that grows from an unhealthy scalp is at a disadvantage from the start.