This is the 4115th most frequent Polish word.
bezmyślne
"Bezmyślne" means "thoughtless" or "mindless" in English.
In this sentence, "bezmyślnie" is used as an adverb to describe an action performed without consideration.
To było bezmyślnie zrobione.
It was done thoughtlessly.
Here, "bezmyślne" is used as an adjective to describe actions that lacked thought or consideration.
Ich bezmyślne działania doprowadziły do problemów.
Their thoughtless actions led to problems.
In this example, "bezmyślnych" (genitive plural) modifies "decyzji" (genitive plural of "decyzja") indicating a general state of lacking thought.