In the ordinary ebb and flow of business, documenting the terms on which deals are struck is not always at the forefront of the minds of those involved: precisely documented terms are, after all, not the main object of the deal and can even be viewed with suspicion (as preventing business, rather than helping it).
When business is going well, no one is particularly worried. Then a problem arises: a payment is not made; a product/service is alleged to be defective; a party does not perform as expected...
