This is the 11568th most frequent Russian word.
дураку
"дураку" means "to a fool" in English.
The word 'дураку', in the dative case here, refers to a fool and conveys the idea of someone to whom the purpose is not clear.
Только дураку не ясна эта цель.
Only a fool does not understand this purpose.
Here, 'дураку' is used in the dative case, indicating to whom the help is being directed, namely the fool.
Помоги этому дураку собрать свои вещи.
Help this fool pack his belongings.
In this sentence, 'дураку' again appears in the dative case, symbolizing the person receiving the truth, the fool.