The results of the code depended on the timing of the code's execution. If both threads entered the critical section at roughly the same time, surprising outcomes could occur.

The code used a shared variable between two threads, so the variable must be passed between threads through a disk-swap. The race condition is the race for the disk-swap to complete before the counter can be updated again, as if unsuccessful, it can lead to surprising results.

Both threads race to finish first as we cannot guarantee that the thread created first will finish first depending on OS scheduling.

The code contains a critical section and any time there is a critical section, a race condition arises.