Copium is the joke word for motivated-reasoning after the fact. It covers the whole family: it is only a loss if I sell, the timeframe was always longer, the market is wrong, this is accumulation.
The word is useful precisely because it is mocking. Naming your own copium out loud is a crude but effective form of affect-labelling, and communities that use it on each other tend to cut losses faster than ones that offer sympathy.
Related: hopium, motivated-reasoning, denial, bag-holding-psychology