What does it mean to "be careful and reasonable" when using drugs? Especially the first time. After all, the effect of the first try is unpredictable?

In addition to the above, it will be reasonable and careful to learn about the possible consequences of taking a particular psychotropic drug, read trip reports, find out if you and your relatives have hereditary mental illnesses, if you are taking drugs that are incompatible with the substance, and to be able to get rid of unwanted effects (for example, when taking psychedelics, it is advisable to have antipsychotics and traquilizers in the medicine cabinet in case of an overdose or bad trip).
But in general, non-medical drug use is always a risky and irresponsible business, because it is not for the sake of risk and excitement, including people accept them?

Well, I'm afraid the analogy with alcohol is not entirely appropriate. Especially when it comes to the same spice. Read thequestion.ru

Where the guy, who first tried spice, thought he was being chased by a fire-breathing dragon. And then the guy thought that his wings had grown, and he tried to fly away from the dragon through the 6th floor window.

It all depends on your body and mental state. It is impossible to predict how your body will behave. When taken for the first time, this means taking a medium or even small dose. Also, some part depends on the group of drugs, and what you expect from them.