What exactly does otherwise mean? What are the other wises? wise means manner/extent.
O'Sullivan & Hilliard's The Law of Contract (2018 8 ed). p 106.
5.55 Furthermore, there are several more general problems with the decision in [Roffey]:
• Fear of duress might not be the only reason for the rule in Stilk v Myrick: it may also operate to encourage parties to price their contracts properly in advance. As O’Sullivan (1996) points out: ‘Why should any contractor bother to estimate his price accurately or supervise his staff, now that the law is willing to treat his
difficulties in performing his contractual obligations as a sufficient “reason” for enforcing a subsequent promise to pay him more than the contract price?’
• Those who criticise a consideration requirement in this context point out that many contracts, rather than embodying a one-off transaction, are in fact long-term relational arrangements, which must be allowed to develop with the parties’ relationship over time. In such cases, the requirement of consideration for each variation is unrealistic and, it is said, should be modified to meet commercial reality. One response is to say that, if properly drafted, such relational contracts can contain their own mechanism for alteration over time (like a rent review clause in a long commercial lease). But more fundamentally, of course, the point is that Roffey was not such a contract anyway—it was a one-off job for a price.
• Commercial parties need certainty. Supporters of the Roffey approach say that it is nonsense that a contractual variation is enforceable if the other side’s obligations are altered in a trivial way, but not otherwise. But that is at least a fairly straightforward way of making the variation work, allowing for clear legal advice at the time and thus avoiding litigation later.
• Finally, it should be noted that those who advocate the abolition of consideration for contractual variation do not necessarily agree with the approach in Roffey that practical benefit suffices for consideration. For example, the New Zealand Court of Appeal has since gone further and decided that contractual variations, once relied on, do not need consideration at all (see Antons Trawling Co Ltd v Smith (2003), noted by Coote (2004)).