Subjective claim

Hello Rabbi
I saw that you talk a lot and write in your book about the disadvantage of a subjective claim.
I wanted to ask if there is a fact that cannot be verified (all crows in the world are black), is it possible to make a subjective claim?
In cases where the truth is clearer, such as there are crows, I see the weakness in a subjective claim, but in cases where it is impossible to verify in any case, what is the disadvantage of a subjective claim? After all, in such a case, both an objective claim and a subjective claim cannot be compared and verified.
Thank you very much!