Myth check
Third tone must always dip then rise.
The full dip-rise appears in isolation; in phrases tone 3 is often low.
Verdict
mixed
Why
Before another tone 3, the first usually rises (sandhi) Keep evidence from your own listening and speaking practice, not from fear stories.
Over-dipping every third tone can sound unnatural Keep evidence from your own listening and speaking practice, not from fear stories.
Textbooks may still mark original tones Keep evidence from your own listening and speaking practice, not from fear stories.
Test the better framing with a short practice drill the same day you read this myth.
Better framing
Learn citation shape, then practice low third tone in phrases.
Practice tip
Practice tip: after reading “Third tone must always dip then rise.”, do one concrete drill from the better framing—speak aloud for five minutes using related words or tones.