"An ounce of prevention is worth a pound of cure." — English Proverb
Generally the most effective way to achieve quality is to avoid having defects in the first place. It is much less costly to prevent a problem from ever happening than it is to find and correct the problem after it has occurred. Focusing on prevention activities whose purpose is to reduce the number of defects is better. Companies employ many techniques to prevent defects for example statistical process control, quality engineering, training, and a variety of tools from the Lean and Six Sigma tool kit.
Start with the idea of preventing defects, not waiting until they are identified and correcting them. Many companies have an active Zero Defects policy where defect prevention is paramount and quality inspection is almost just a verification of what they already know – that the product is defect free. If we can start with quality and maintain that quality throughout the process we will have a quality product.
Quality must go beyond our product specification or contracted service. We cannot add it at the end of the line or inspect it into the product. At best that is only a false sense of security. If we want a quality product it must be made with quality processes by quality minded people. A focus on quality must be intrinsic to the company culture and practices for the customer to take notice.
Quality is about prevention—you cannot "inspect" quality into a product. It has to happen before the inspection process.