Parmenides made a logical argument against the possible existence of change. An excellent restatement of the argument was offered by Bertrand Russell in his A History of Western Philosophy:

“When you think, you think of something; when you use a name, it must be the name of something. Therefore both thought and language require objects outside themselves. And since you can think of a thing or speak of it at one time as well as another, whatever can be thought of or spoken of must exist at all times. Consequently there can be no change, since change consists in things coming into being or ceasing to be.”

Parmenides is saying that to believe in change is illogical and to believe something illogical is wrong and bad practice.

This article, section b. Reality gives a more detailed breakdown of the argument by Parmenides that change is illogical. https://iep.utm.edu/parmenid/#SH2b