The chance of two people hearing the same message and understanding it in the same way is highly unlikely.

In a perfect world with perfect communication between people, you will always be understood, however, this world is far from perfect and communication between people is less than that.
What she said and what she meant very rarely matches what he heard her say and what he thought she meant. “I’ll be ready in five minutes.” –Open to debate.
All you can do is hope people will understand you.