This summary is not the rule. The rule text controls.
If someone testifies in court, they have to actually know what they're talking about firsthand. This means the person needs to have seen, heard, or otherwise directly experienced the thing they're describing. They can't just repeat rumors or guess at what happened.
Before a witness can share their account, there has to be enough proof that they really do have this firsthand knowledge. The witness's own statement that they saw or heard something can count as this proof, but it doesn't have to be the only evidence. Other facts or testimony can also show the witness was in a position to know what they claim to know.
There's an exception for expert witnesses. Experts like doctors, engineers, or accountants often give opinions based on training and experience rather than personal observation of the specific event. Rule 703 covers how that works, so this personal knowledge requirement doesn't block expert testimony in the same way it does for regular witnesses.
