sorry... as an example of true beliefs that might not be so useful...

there was a study (sorry can't recall reference) that found that people with depression tended to have more realistic self-assessments than people who had more healthy self esteem.

it might possibly be the case that reflecting too much on current assessments...
leads to depression (ie is not useful to focus on)
even though...
some of those assessments are true.

(or it might be the case that considering that those negative self assessments would ALWAYS obtain into the future was what was unhelpful to them...)

anyway... that might be an example of an unhelpful truth... if there are unhelpful truths... then i wonder what should be done about those???