  Theoretical physics has faced many challenges since the advent of quantum
mechanics. Recently, Frauchiger and Renner have presented a no-go theorem,
which makes quantum mechanics more controversial. However, from our
perspective, the process of proving appears questionable. Therefore, we discuss
the validity of their proof approach in this letter. Here, we propose a simple
thought experiment that clarifies how correctly the attributed quantum state
can be written in problems similar to Frauchiger and Renner's
Gedankenexperiment. In the next step, with the help of the correct form of the
quantum state, it is demonstrated that a fallacy occurred in the proof of the
no-go theorem, which means it cannot be valid because of the wrong proof.
Ultimately, getting help from Hardy's paradox, we investigate whether there is
an approach to modify their proof in order to lend the no-go theorem validity.
