How?

Contract law has evolved because transfering the ownership of things is fraught with difficulty. Ownership as a concept itself is notoriously hard to define.

Consider housing - when you buy a house you own that land. Except if its an apartment, you just own the internal walls. Or when the government aquires your land through eminent domain. Or mineral rights - which don't belong to you, you just own the top 5 feet of topsoil. Or if you neglect a property and some squats in it. Or if you were given a fraudulent payment, and they take back the property.

Just getting people to agree is notoriously difficult when people have different often conflicting desires.