It takes a 3rd party, someone outside the situation, and possibly some time after the fact, to decide what most approximates objective truth.

I don't trust myself here and now, I could be drunk or deluded, or vain, or biased, or self-obsessed (most people seem to be that way).

I don't trust my doctors, they could be under-educated, or self-interested to overtreat me, or publish more papers on anti-doctor paranoia, and self-obsessed (most people are that way).

I only trust some averaged, collective, rational, longer-term, reflective, investigative, independent, reviewed, challenged, criticized and doubted process to get closer to truth.