South Africa President Jacob Zuma’s sacking blunder

To lose one finance minister may be regarded as a misfortune; to lose two looks like carelessness, and President Jacob Zuma’s decision to get rid of two finance ministers in less than a week has been a colossal blunder.
He sacked the respected Nhlanhla Nene in a surprise move on Wednesday evening and replaced him with the little-known David van Rooyen.
Not only was this seen as a blunder by opposition parties, who called for his resignation, but also by the general public and the financial markets
The president acknowledged his initial mistake, hence the change of mind and the appointment of the experienced Pravin Gordhan.
But why in the first place did the president fire the seemingly competent Nhlanhla Nene?