In Parshas Tazriah we learn the halachos of negoim (literal translation blemishes)through which one can become tameh if the Cohen determines (paskens) that it is a genuine nega. One of the halachos of negoim is, “ein adam roeh nigai atzmo” (one can not see [and determine the status of] blemishes that they themselves are afflicted with). Rav Pam pointed out that this is both to say that it is tahor and to say that it is tameh that one can not pasken about himself. The kadmonim say that this rule applies not just to the laws of tuma and teharah, but to all blemishes.
Sometimes people think poorly of themselves and walk around depressed because of something they did wrong or a shortcoming they perceive about themselves. They should know that can’t judge their own blemishes and shortcomings and they have no business “paskening” on themselves that they are “bad”.