The deposit you will not get back
Two months' rent, handed over in cash, held by the person you are least able to compel. The tenancy is the most common contract on earth and one of the least enforceable.
You paid two months' rent as a deposit when you moved in. Three years later you move out, the flat is clean, and the answer is a shrug: there was a mark on the wall, the boiler was serviced, the money will come next month. It does not come. You can sue, and for two months' rent you will not. Everyone in this story knows that, which is why the story ends this way.
The tenancy is the most widespread contract there is. It is also one of the least enforceable: rent is paid in advance to someone who has already been paid, the deposit sits with the party you have no leverage over, and every clause about repairs and notice is a sentence in a document that only becomes real if a court reads it. Landlords are not villains here. Bad tenants exist too, and their landlord is equally unable to collect for a wrecked kitchen. The contract simply has no enforcement layer, so both sides carry the risk of the other's character.
What changes
The deposit stops belonging to either party. It is locked in escrow at the start of the tenancy, not the landlord's account, not the tenant's: the tenancy's own. Neither can move it alone. At the end, it releases on whichever rule the parties agreed to at the beginning: automatically after a clean handover, or split by the arbiter named in the contract before anyone had a dispute to argue about.
Rent becomes a flow, not a monthly errand. It moves on schedule from a committed source. Nobody chases, nobody claims they paid, nobody claims they didn't, and the record of thirty-six on-time payments is the tenant's own portable credit, worth more to them than any reference letter.
Conditional terms actually run. "One month rent-free if the tenant repaints" is today a handshake and tomorrow a dispute; here it is a rule with a condition. So is the escalation clause, the notice period, and the refund on early termination. What was a promise becomes a branch.
Notice what this does to the balance of power: the party with less leverage stops needing leverage. That, and not efficiency, is the point.