Shift-left is an approach to software development and operations that emphasizes testing, monitoring, and automation earlier in the software development lifecycle. The goal of the shift-left approach is to prevent problems before they arise by catching them early and addressing them quickly. 

When you identify a scalability issue or a bug early, it is quicker and more cost-effective to resolve it. Moving inefficient code to cloud containers can be costly, as it may activate auto-scaling and increase your monthly bill. Furthermore, you will be in a state of emergency until you can identify, isolate, and fix the issue.