The transactions need to take their due course, irrespective of what is happening
in the system at the same time. One of the important ways that this is used is
in the example where one transaction is writing to the database and another
is reading from it. In an isolated database, the read transaction cannot know
about the write that is occurring "next to" it until the transaction of the write
operation is complete and fully committed. As long as the write operation is
not committed, the read operation will have to work with the "old" data.