Earlier quoted context omitted.
That's not the case no, you usually access your database with thread pool. Otherwise everyone would wait until the single connection is free. Once you have a bit more users that tries to write everything will fall appart.
Well, let me throw out a crazy idea: Nobody said you have to use a single database/file. Obviously, you are going to want to spend a couple minutes thinking about referential integrity. But how often do you delete records in your web app?
As an IRC client with an SQLite backend: several hundred times per second.
Per user.
While reads are more like once every day per user.