Whether buying a house or haggling over the price of a plumber, good negotiators know it's savvy not to show your hand too early.
David Cameron has been keeping his cards close to his chest as he tries to broker a new deal for the UK ahead of the upcoming referendum on its membership of the EU.
The prime minister has set out four broad areas where he's seeking change - the UK's sovereignty, access to benefits for migrants, the EU's competitiveness and the rights of countries outside the Eurozone.
But he's steered clear of revealing exactly what he wants or how he hopes it can be achieved. Now, amid a growing chorus of frustration from EU leaders seeking more clarity, Mr Cameron has agreed to put his wish list on paper - and by a set deadline.
In a few weeks time, the prime minister will write to the President of the European Council, Donald Tusk, setting out his demands for reform.
The letter, according to Downing Street, will be shared with EU leaders, UK MPs and the public. No 10 says this is a natural stage in the process to allow more detailed discussions - but there's a danger for Mr Cameron.
If his demands are strong enough to satisfy Eurosceptics it's unlikely they'll be agreed by EU leaders. If the proposals stick to achievable reforms it is unlikely they'll appease Eurosceptics.
There's no doubt such a document would have been produced at some point and was unlikely to please all, but it is scrutiny Mr Cameron may have hoped to avoid at this stage.
He might choose to keep it vague rather than produce a finite list for which he could be held to ransom.
But the fact this letter is being written at all shows that EU leaders aren't prepared to let the UK alone dictate the terms of this negotiation.
The European Commission President Jean-Claude Juncker said of the referendum talks; it takes two to tango. Anyone for steel-capped dancing shoes?