Every single couple of weeks, there is legal news in which a medical malpractice case that went to a trial, resulted in a verdict in favor of the plaintiff, was reversed on appeal, and then tried again - this time, for a a lot larger verdict in favor of the plaintiff. This article discusses why that occurs.
At a tort (negligence, malpractice, breach of fiduciary duty, wrongful death, etc.) trial, the defendant normally holds most of the cards. They typically know which stones you overturned on discovery and which ones you did not, and they know which evidence that you have his most embarrassing and which evidence you do not have is most absolving.
Far more importantly, they were there. They genuinely know what they did and did not do, and what they were thinking when they did it, and they surely know what they intend to say. In a medical malpractice case, that portion is necessary, since the patient frequently has nothing much more than the medical records ready by the physicians themselves. Think of a medical malpractice case in which a sponge is left in a patient - in a subsequent lawsuit, the patient knows absolutely nothing extra than what the surgeons and nurses wrote on the records.
It does not matter how many depositions you took -- you could have had people testifying for days -- and how much written discovery you collected, trial will nonetheless be full of surprises. Even if no new facts are revealed, you will see facts presented in a new light, typically at odds with the light they were presented in pleadings and throughout discovery. (And you will have to speedily react to this new version of the truth: do not even try to argue to the jury that a reality was "presented in a diverse light in the course of discovery.")
Trial makes the defendant show their cards, clearing away their natural benefit in a tort suit. You will see the strongest defense arguments and the most favorable defense evidence. A lot more importantly, though you can generally run a mock jury and see how neutral non-lawyers react to your evidence, you will by no means get a likelihood, pre-trial, to practice cross examining a defendant to see what evidence makes them squirm, babble, or obviously lie. A deposition will give you hints, but it will never show you what will truly make a defendant fold or what they'll do when the chips are down.
My view is that these big situations are not 50-50 or longshots, they're slam dunks if you have all the evidence, know exactly where the defendant wants to go, and know where the defendant doesn't want to go. That's how a "massive" verdict becomes a "blockbuster" verdict the second time around.