Animal trials precede the first (Phase I) clinical trials in people.
93% of drugs that make it past animal trials and into Phase I clinical trials fail to make it all the way to final approval:
https://blogs.sciencemag.org/pipeline/archives/2019/05/09/th...
It's also not clear how many drug candiates we're missing out on because animal models give false positives for toxicity in humans. Compounds that are extremely poisonous to experimental animals may be tolerated much better in humans.
Humans survive exposure to TCDD at levels that would be more than 50 times higher than the lethal dose in guinea pigs:
https://en.wikipedia.org/wiki/2,3,7,8-Tetrachlorodibenzodiox...
Acetaminophen is a deadly poison to cats even at modest doses.
It's impractical and unethical to try novel druglike compounds in humans right away, so we may not know how many premature rejections come from animal models until/unless we're able to grow whole human organs for drug testing.
And keep in mind we're talking here about behavioral differences driven by possibly the most complex organ that diverged the most from other animals'.
Isn't the point of doing animal trials that they are "close enough" for most things to deliver good results? I.e. "if you can't do it in mice, dogs and pigs with your proposed medication, you probably won't be able to do it in humans". They're close enough that xenotransplantation is actively considered. "Humans are so special, everything we learn about anything that isn't human does most likely not apply to humans, so don't you dare even suggest that" just sounds strange to me.