How Not to be Fooled by Time Series Models

It is easy to be tricked by time-series models. I have seen models that are able to (seemingly) predict the most random trends accurately, such as stock and crypto prices, using advanced techniques that most don't fully understand. Is time series really like magic in this regard? Perform the right data manipulations, apply a complex-enough model, and presto, amazingly accurate predictions are produced for any date-indexed line into the future? If you have seen the same things I'm describing and are skeptical, you are right to feel that way.