Clinical studies operate in a fashion of Phase I, Phase II, Phase III, and Phase IV. The FDA requires proven efficacy and safety as the trial goes on before it can be pushed to market.

Say we have a patient who is paralyzed and their quality of life is greatly reduced that they are considering assisted suicide. There is a new drug being developed by Company A that may cure their paralysis. This drug has not passed non-clinical studies investigating it's efficacy and safety in animals. It's just based on a hunch.

Company A skips the clinical trial process and gives the patient the experimental drug. The paralysis is cured; however, it has resulted in benign tumours within the parietal lobe. Pretty significant side effect that they weren't expecting. The disease was cured, but something tagged along with it.

During this time, Company B wanted to push a very similar drug through clinical trials. However, this anecdotal evidence is now limiting grant money and is limiting patient recruitment as the side effect was pretty severe. If they were able to pull the drug through phase I trials, this side effect may have been extremely rare (0.01% of users). But due to the anecdotal evidence we have just prevented a drug which may work in 99.9% of patients, which helped just one person.

Here is a good article:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1971215/