Cooperation is secured on unwritten understandings that both sides know are unwritten, trading on trust and reputation where a contract would be slow, awkward, or impossible.
Borderline: whether this move is justified depends on the situation, and only the person in it can judge.
An example
The operating chief of a private-equity-backed services company needed every branch on the new dispatch and billing system by year end, ahead of a planned sale, and the founder who ran the largest branch was the main holdout. Over dinner the operating chief said plainly what he could and could not offer. He could not promise a role after the sale, since the buyer would decide that, but he would tell every bidder that the founder had carried the hardest conversion in the company, and he would push for a regional role if one existed. The founder said he understood it was a handshake. He moved his branch onto the system in eight weeks. The operating chief told both bidders about the work, and the buyer asked to meet the founder about the western region.
Why it works
An unwritten understanding makes cooperating look better, because it carries a real prospect of help that formal channels could not offer. It makes cooperating easier, since nothing written means little exposure and no awkward negotiation. Insisting on paper becomes the costly path in that register, because it signals distrust or unfamiliarity with how things work at this level. For this to work, someone must hold real discretion over future help, the counterpart must value the relationship, and the culture must let reputation enforce what contracts do not.
The thinking behind it
Robert B. Cialdini In Influence (1984), Robert Cialdini describes reciprocity, the obligation people feel to repay what others give them. An unwritten understanding runs on that obligation, with each side's help creating a debt the other is expected to honor without a contract. It explains why handshakes work among people who will deal with each other again, and why a single unhonored one damages the person who broke it.
Oliver E. Williamson Oliver Williamson's Markets and Hierarchies: Analysis and Antitrust Implications (1975) holds that bounded rationality makes every agreement incomplete and that some parties will exploit the gaps, which he called opportunism. An unwritten understanding is as incomplete as agreements get. The clean form answers it by stating plainly what is and is not offered, and the person receiving one should treat any undocumented reward as unpromised.
When it fits
Relationships where a contract would be slow, awkward, or impossible suit it, such as cooperation on a change, support before a decision, or help around a sale, and where both sides will deal with each other again. You need a reputation for honoring understandings and real discretion over what you offer. It fails with counterparts who need documentation, such as auditors or lawyers.
How to use it well
State exactly what you can and cannot offer, out loud, since the understanding is only as good as its clarity.
- Promise only what lies within your own power: your effort, your word to others, your advocacy.
- Name what you cannot promise, especially anything a later owner or committee will decide.
- Check that the other side heard it the same way; a short note restating it is fine if they want one.
- Deliver visibly, and soon.
Your record of honoring handshakes is the collateral, so keep it clean.
What it costs and where it backfires
If you misjudge what you can deliver, the other side will feel cheated whatever you said, and the story will travel. Unwritten deals favor whoever holds the discretion, so counterparts with less power may come to resent the arrangement. The line is the promise you know you will not keep. Hinting at a reward you cannot or will not deliver, to get cooperation now, is a lie, and doing it once ends your ability to make handshakes at all.
When it is used on you
Commitments made to you only in one-on-one conversations deserve a short written summary of what you heard, with a request to confirm it. Ask others whether this person has left earlier handshakes unredeemed, treat any reward you cannot document as unpromised, and ask for high-stakes terms, such as a role after a sale, in the documents that govern the deal.