Most people have heard the old saying about assumptions. Something about making something out of you and me. Well it is true. I recently got into a crunch situation with a client and experienced this first hand.
It doesn't matter if it is requirement or team responsibilities. Anything that is not recorded or communicated is a risk. I know that different methodologies have differing opinions on documentation, but in the end all of them seem to agree that communication is the key.
It should be well understood what the client needs to accomplish, the systems involved, partners to the process, and who is responsible for which features. Without these being communicated and understood by all stake holders the risk of something being missed or worse done incorrectly is almost 100%.
Communication also needs to happen early and often. If your team has an issues or risk list, get things on it as soon as they appear. Trying to work them first to full understanding only adds to the risk.
I am filing this under the lessons learned and don't let this happen to you categories. Experience can be a brutal teacher.