This summary is not the rule. The rule text controls.
An expert witness can share their opinion in court without first walking through every fact or piece of data that led to that opinion. They can just state their conclusion and explain their reasoning in general terms. This makes it easier for experts to testify without getting bogged down in long, technical explanations before they even get to the point.
There's a catch, though. If the other side asked for this information earlier during discovery (the fact-finding process before trial), the expert had to hand it over then. So this rule doesn't let anyone hide information that was properly requested ahead of time.
Also, even if the expert didn't have to explain their full reasoning during direct testimony, the other side's lawyer can still dig into it during cross-examination. They can ask the expert to explain exactly what facts or data they relied on and challenge whether that basis is solid. This gives both sides a fair shot: the expert can testify efficiently, but their reasoning can still be tested and questioned.
