What was bad about being a peasant in the middle ages?

Most medieval peasants were serfs. Some were free. The situation for free peasants and serfs was different. Peasants were mostly farmers. As farmers, they had places to live and work, which they were less likely to lose than their counterparts in towns and cities were. In addition, for serfs, the place to live and work were guaranteed by the manorial system, as rights. Serfs were also supposed to have a right to protection in times of war or famine - the lord was legally obliged to provide these things.

Disadvantages included a lack of social mobility. Peasants did not normally get educated, and did not have an easy way to improve their lives. Again, for serfs, they were obliged to remain at their jobs on the manors, and could not legally leave. They were said to be bound to the soil.

There were times of unrest in Europe when free people gave up their freedom to become serfs on manors, because they would otherwise starve or be somehow otherwise destroyed. The protection serfs got was very important when things were bad.