Core answer
Start here. This is the direct spoken answer to practice first.
Overview
The top-level context error is often a wrapper; the useful evidence is the deepest actionable cause and the configuration path that produced it.
I preserve the complete startup log and find the deepest meaningful cause rather than stopping at ApplicationContext failed to load. I classify the failure: configuration binding or validation, missing or ambiguous bean, circular dependency, port conflict, classpath incompatibility, database migration, or an external call made during initialization. Boot failure analyzers often provide a focused description and action. For conditional configuration, I enable or inspect the condition evaluation report.