When Americans make an agreement, they want the terms clearly stated and preferably documented. This starts in childhood with allowance arrangements and continues through every major commitment in life. The expectation is that important agreements get written down—not because people distrust each other, but because clear documentation prevents misunderstandings later. You will encounter this in job offers, contracts, policies, and even social arrangements.
The phrase “get it in writing” reflects practical wisdom, not cynicism. When you reach an agreement with Americans, expect to discuss terms explicitly and create some record of what was agreed. Vague understandings make Americans uncomfortable because they know that memories differ and disputes arise. Documentation protects everyone by establishing what was actually agreed.