Deploying HTTPS often seems simple: point a domain to a server, use a reverse proxy like Caddy, and let Let's Encrypt handle certificates. However, certificate issuance repeatedly failed despite correct configurations. The problem was not with Caddy, but with a misunderstanding of how ACME domain validation works. The initial assumption was that the server reaching Let's Encrypt was sufficient, but the crucial connection is Let's Encrypt reaching the server. Let's Encrypt uses ACME to verify domain ownership through validation challenges. Logs revealed that specific validation steps were failing, not just a general certificate failure. This highlighted that HTTPS failures are often underlying networking issues like DNS, routing, or firewall misconfigurations. A systematic debugging approach is more effective than random configuration changes. This involves verifying DNS, checking port accessibility, inspecting ACME logs, and confirming challenge responses. The key realization was that ACME is a validation protocol, not just a certificate issuance feature. Understanding this shift in perspective, from "why won't it issue" to "why is validation failing," is essential for successful debugging. Replacing assumptions with a thorough understanding of how ACME operates is the most effective way to resolve certificate issuance problems.