It happens often when "error" field is not a bool, but a string, aka error_message. Could be empty string, or _null_, or even _undefined_ if we're in JS.

Then the obvious question why do we need _succeeded_ at all, if we can always check for _error_. Sometimes it can be useful, when the server doesn't know itself if the operation is succeeded (e.g. an IO/database operation timed out), so it might be succeeded, but should also show an error message to user.

Another possibility if the succeeded is not a bool, but, say, "succeeded_at" timestamp. In general, I noticed that almost always any boolean value in database can be replaced with a timestamp or an error code.