As can be seen from the diagram, if the green philosopher holds fork 1 and 2, then the yellow philosopher (for example) is unable to eat as he cannot grab fork 1, only fork 5.
Such an arrangement might lead to a deadlock as each philosopher might hold one of their forks, but are unable to grab the second fork because it is already held by someone else. As all philosophers are waiting for someone else to drop a fork the system deadlocks and no philosopher will be able to grab a second fork or drop the current one they hold.
Using this problem I'll show the cause of the deadlock and by preventing the Coffman Conditions, one by one, show how the application no longer deadlocks.
But let's start at the beginning with an application that does deadlock.