Lawyers and, occasionally, judges may think that the equitable jurisdiction of the courts is simply an exercise of judicial discretion to avoid a result that seems unfair to somebody. The Privy Council usefully reminds us in Cukurova Finance Int'l Ltd v Alfa Telecom Turkey Ltd, [2013] UKPC 20, that in 'no way' should it be suggested 'that equity recognises any general or open-ended discretion'; equity proceeds instead on the basis of principle and well-settled (if sometimes not always clearly articulated) rules. 

At issue in the case itself (on appeal from the courts of the British Virgin Islands) was whether relief from forfeiture was available to assist a party which had granted another the right to appropriate charged shares in order to satisfy liabilities under a financing agreement, the party subject to the forfeiture having initially defaulted but then subsequently tendered the full amount payable (which the other party rejected). The judicial committee disagreed whether relief from forfeiture was available on the facts: the majority said yes on the grounds of unconscionability and 'special circumstances'. Lord Neuberger and Lord Sumption said no, since granting relief would essentially extend the term of the loan; any relief from that should be in accordance with the terms of the agreement, the majority's invocation of 'special circumstances' being dangerously uncertain and a departure from the 'fixed principles' of equity. For Lord Neuberger, the majority risked treating 'unconscionability' as 'a panacea for adjusting any contract … when it shows a rough edge to one side or the other', which he thought ill-advised.

http://www.bailii.org/uk/cases/UKPC/2013/20.html