Secure by design means security decisions are made while the system is still being shaped, not after the product has already grown around risky assumptions.
That starts with threat modeling: understanding who might attack the system, what they would want, and which paths give them leverage. From there, architecture, access control, logging, deployment, and review practices can support the same security model.
Good security also stays practical. Teams need controls they can maintain, alerts they can understand, and response plans that make sense under pressure.
