The SQLite website (https://www.sqlite.org/) uses SQLite
itself, of course, and as of this writing (2015) it handles
about 400K to 500K HTTP requests per day, about 15-20% of
which are dynamic pages touching the database. Dynamic
content uses about 200 SQL statements per webpage. This
setup runs on a single VM that shares a physical server
with 23 others and yet still keeps the load average below
0.1 most of the time. Generally speaking, any site that gets fewer than 100K
hits/day should work fine with SQLite. The 100K hits/day
figure is a conservative estimate, not a hard upper bound.
SQLite has been demonstrated to work with 10 times that
amount of traffic.
If SQLite is able to comfortably handle 100k hits/day, I imagine that more "legitimate" databases can handle more traffic comfortably without needing to jump to scale horizontally.
For example, someone might dismiss IDEs as being unnecessary because technically the same job can be done without them by a superior human being, so the solution is to just be a superior human being.
Or as another example, someone could completely dismiss syntax highlighting as being useless for the superior, implying that the solution to the problem syntax highlighting solves is to just also become a superior human being.
There are multiple layers to any solution, and if one of them is missing, the others are kind of shaken out of balance.