Postgres, error in tutorial?

Yesterday, I got a help request, about PostgreSQL. Can't develop much about it as the question was really unclear and I had problems on my own.

Every time I tried to use psql, I'd get:

psql: FATAL:  database "cayalame" does not exist

And I thought I had a complete and reliable PostgreSQL installation. I checked the tutorial I used, here. And it detailed:

createdb cayalame_db

but I already had that database in the system. After checking if user valid and creating again the database, I chose to create the database with the requested name. And voilà, Postgres working for the user.

Just to keep in mind, not to blindly follow instructions.