Developers often hit CORS errors when their browser blocks requests between a frontend and backend. This happens because the same-origin policy is a fundamental browser security rule preventing scripts from one origin, like `tejaswahinduja.me`, from accessing data on another, like Instagram, even if you're logged in.

Cross-Origin Resource Sharing (CORS) solves this by letting servers explicitly permit trusted origins. The backend sends an Access-Control-Allow-Origin header in its response, telling the browser which clients are allowed. For non-standard HTTP methods like PUT or DELETE, the browser first sends a preflight request to check permissions.

While frustrating, CORS is essential for web security, preventing malicious sites from accessing your private data. Properly configuring it is a core task in building full-stack applications, ensuring safe communication between your client and server without compromising user security.