Saccharin was discovered when Ramsen rolled a cigarette and noticed that the paper tasted sweet (there is a non-tobacco version of this for the faint of heart).
And Alexander Fleming discovered penicillin because some bread from an old sandwich did not become moldy.
Modern lab procedures preclude any such discovery today.
Penicillin is mould. Mould has been known for centuries to have special properties that resist infection, but no scientific evidence to back it up.
The bacteria culture was accidentally left open during a vacation and some mold started growing on it. When they returned, it had killed off the bacteria. Fleming isolated the mould (penicillin) and had a provable antibiotic.
Lab errors still happen, though, because they are still run by humans.
And Alexander Fleming discovered penicillin because some bread from an old sandwich did not become moldy.
Modern lab procedures preclude any such discovery today.