I agree with @ibraheemshaikh that you need to also be careful in entering data. It is extremely important and crucial to always double and triple check and always keep a cautious mind.
About clinical research, I had worked for 2 years in a clinical lab and we didn’t have failures but we definitely ran into many issues which are quite common. For example, subjects/participants commitment (they may run late, miss their window, miss their appointments, quit in the middle of the experiment period or just simply change their mind and don’t want to use their data anymore); troubleshooting devices (sometimes, the devices you built just break down, but that’s how you learn); human error (entering data, data analysis mistakes, mistakes in script, error in paperwork, IRB forms leading to freezing the projects etc…)…There can be many many challenges so our rule of thumb is to always have a checklist, always double checking, always ask questions and keep organized.

About pre-clinical research, I have interned/worked in this clinical lab and we tested chemo drugs on various cancer cell lines. For various cell lines, even though the drug showed a potential reduction in tumor size and weight previously in colon cancer after retested, it just didn’t work as well for all types of cells such as breast cancer or lung cancer. I guess that’s just how research is, full of trials and errors until you find the cure.