Medieval communities were very structured.  Everyone knew their place and what was expected of them.  They knew that they had to pay for their land with services to their lord, they also knew that they had to pay taxes (or fines) to him when they or their children married, when they inherited land and when the king commanded it they knew that they had to fight with their lord.

For more on life on a medieval manor read The Seeing Stone by Kevin Crossley-Holland