To demonstrate a more complex problem with lifetimes, let's consider a mythical bank account:

• I am given access to a bank account, legally, of course
• I decide that I want my friend to have access to it
• After a certain amount of time, I decide I no longer want access to the account and have my access removed
• My friend then tries to use the account

When my friend comes to use the account, he is unable to do so, as the reference I had, and which was passed to him, no longer exists. He is trying to use after free (in programming terms) and he is known here as a dangling reference.

It sounds far-fetched, but in development terms, it happens far more frequently than you would possibly give credit for.