2015 was an amazing year for Jeremy Corbyn - but many would agree that mistakes have inevitably been made. One of the most glaring – most public – was Corbyn’s decision to people his Shadow Cabinet with appointments selected from across the spectrum of opinion in the Parliamentary Labour Party.

Natural allies were kept waiting in the wings while dissenting voices were invited upon the stage. They were given the time and opportunity to come together in a chorus of unity. This did not happen.

No doubt the vast majority of commentators believe this to be Corbyn’s fault. That he wasn’t enough of a unifying figure or flexible enough to meet the different expectations of cabinet members and the wider party. But the Labour Party is a broad church and the reality is that a contortionist would have failed to meet such requirements. Still, it’s a mistake not to be repeated.

There are rumours of a New Year’s Shadow Cabinet reshuffle and it would be easy to frame this in terms of revenge and resolution. While it is hard to imagine the Labour leader unaffected by the betrayals of past weeks, it is more likely to be another piece of the puzzle that is Corbyn the leader. The cabinet appointments can be viewed less political mistakes than failed experiments.

Experiments are performed to see what works and what doesn’t. Corbyn received some predictable results but his willingness to explore such possibilities is the mark of a man who wants to get it right. They are the actions of a future leader, not those of a man who merely wants to give the appearance of being one.

As the months go by and a new kind of politics emerges from the fug of political and press hostility, the public are increasingly exposed to Corbyn’s positive qualities – in this case, fairness. It is a quality people on both sides of the political spectrum admire. It is present in the best of our everyday decision-makers: the judicious magistrate; the fair but firm teacher; the impartial parent. It should be present in the words and deeds of our political leaders, but rarely is.

Corbyn was fair in his appointments to the Shadow Cabinet – even down to the pursuit of gender equality. A number of those appointed, however, have not been fair in return. Rather than commit to the debate and dialogue Corbyn so desperately wanted, several briefed against him and made public their disagreements with the leader who had empowered them. Like naughty children at home or in the classroom, they were given extra responsibilities and they abused them.

This was particularly apparent during the Syria vote a few weeks ago, where Corbyn demonstrated his fairness once again in offering Labour MPs a free vote. In voting with the Tories and rallying around an entirely contradictory argument - as presented in a speech by the Shadow Foreign Secretary Hilary Benn – certain members of Corbyn’s cabinet made it painfully clear how they were going to repay their leader’s faith in them.

Chief among these was Benn himself, the true architect of the vote’s success. Benn is an opportunist who pushed himself to the fore and whose actions have come closest to splitting the party. If the Parliamentary Labour Party was a ship, then Benn would be chief mutineer – a would-be captain without the authority to lead beyond a very public gun to his leader’s head. This has been emphasised further by media attention to Hilary Benn’s speech and a number of commentators heralding him as a future leadership candidate, despite the fact that he has been an unremarkable public servant up until now.

Benn and his supporters would have the Labour Party be nothing more than a photocopy of a photocopy. A party of diminishing returns, unwilling to learn the lessons of the recent past and intent on further losing its grasp on what it means to be an actual Opposition. It might simply be an inconvenient truth that these people find it easier to agree with a person like David Cameron than a person like Jeremy Corbyn.

But, like the good teacher or parent, come the New Year, Jeremy Corbyn will need to be both fair and firm. He has given divisive members of the Shadow Cabinet the opportunity to prove themselves - and prove themselves they have. They have proven themselves unworthy of their position.

It is time for a reshuffle and to give others the opportunity - whether they agree with their leader or not - to contribute in a more constructive way. As polls bear out, Corbyn increasingly has a sense of which direction the wind is blowing. Like any captain, he shouldn’t tolerate mutineers.