If, after assessing all known variables, a decision is made to undertake a deliberate action, the result of this action can only be termed "mistaken" retrospectively - never prospectively.
Decisions to marry, decisions to change jobs, decisions to raise taxes, decisions to declare war cannot be considered "mistakes", if elected conscientiously after proper evaluation of the variables involved. Whether these decisions eventuate into retrospective errors in judgment may take many years - even decades - to determine.
Chou En-lai, the former prime minister of China who was highly regarded for his intelligence, reportedly, was once asked his opinion as to the long-term effects of the French Revolution. "Too early to tell," he is said to have replied!