Some drugs, like LSD and psilocybin, have a wide therapeutic range in which there is little to no possibility of pharmacologically induced death, while other substances such as Mescaline become dangerous at only a few times their active dose. Accidental overdoses happen to everyone who works with psychoactives for long enough and overdoses of research chemicals have unknown consequences. If you aren't prepared to accept these risks, you should avoid research chemicals. This research chemical is very similar to a well known drug which is very safe. In the case of a new drug which is very chemically similar to another well known drug, pharmacologists can try to extrapolate from the known drug, but there's no guarantees here.
Idiosyncratic reactions are a large part of the risks taking psychoactive drugs.
Less tested psychoactives may cause extreme or negative reactions in a small portion of users and just because a few people use a chemical recklessly without getting hurt doesn't mean that will hold true for you. People react differently to different drugs. With well known drugs, enough people have done them that we have a pretty good idea what the range of common and uncommon effects are. With research chemicals, there are often many contradictory reports, and its hard to say what the typical effects are simply because not enough people have taken them for us to know what the average results are. What are often the particularly dangerous effects are those that hit a minority of users and this information is not available for research chemicals.