What common mistake do developers make with Constructor injection, why does the mistake cause problems, and what is the safer approach?

What common mistake do developers make with Constructor injection, why does the mistake cause problems, and what is the safer approach? One recurring problem with constructor injection is applying it without understanding the boundary it protects. Resolving every dependency manually with new inside business classes, which makes configuration and testing harder. In addition, A class can declare dependencies in its constructor and let the framework resolve them. Safer engineering approach: keep the responsibility in the correct layer, use the framework's supported API, validate and authorize inputs, avoid hidden side effects, and verify the behavior with tests.