Let's use an example. Monica pays the landlord $500 as a security deposit as required by the lease for the apartment she is renting. If she causes no damage, she has a right to the $500 at the end of the lease. She gave up an asset (Cash of $500) but has another asset: the right to $500 at the end of the lease. The landlord receives the $500, but has an obligation to return the security deposit at the end of the lease. The landlord received an asset (Cash of $500) but has a liability to return the $500 at the end of the lease (unless there are damages).
As the example showed, a security deposit is an asset for one party and the same security deposit is a liability for the other party.
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