Why is understanding the terms of a contract important for both parties involved?

a.
understanding the terms of a contract is important because a person must be certain of the obligations towards the other party, and must also be aware of penalties incurred if those obligations are not met.
b.
understanding the terms of a contract is only important for lawyers, and should only ever have to be signed and not read.
c.
understanding the terms of a contract is important because people involved in contracts are almost always taken to court, and must know the contract to give a good defense.
d.
understanding the terms of a contract is only important when the other party seems shady or untrustworthy.