Error messages can sometimes be cryptic, and you may be left wondering why did this error happen at all?
For this purpose, psql recognizes two variables, VERBOSITY and CONTEXT; valid values are terse, default, or verbose for the former, and never, errors, or always for the latter. A more verbose error message will hopefully specify extra detail, and the context information will be included. Here is an example to show the difference:
postgres=# \set VERBOSITY terse
postgres=# \set CONTEXT never
postgres=# select * from missingtable;
ERROR: relation "missingtable" does not exist at character 15
This is quite a simple error, so we don't actually need the extra detail, but it is nevertheless useful for illustrating the extra detail you get when raising verbosity and enabling context information:
postgres=# \set VERBOSITY verbose