In my experience, the most reliable predictive heuristic that you can use in daily life is something called Regression Towards The Mean. Basically, given that most relevant life events are a result of mixture of skill and luck, there is a tendency for events that are very positive to be followed by more negative events, and for very negative events to be followed by more positive events. This is a statistical tendency that occurs over many events, and so not every good event will be immediately followed by a bad one, but over time, the trend tends towards a consistent average level rather than things being all good or all bad.
Another way to word this is to say that we should expect the average rather than the best or worst case scenarios to occur most of the time. To hope for the best or fear the worst are both, in this sense, unrealistic. The silver lining in here is that while our brightest hopes may well be dashed, our worst fears are also unlikely to come to pass. When things seem great, chances are things aren’t going to continue to be exceptional forever, but at the same time, when things seem particularly down, you can expect things to get better.
This heuristic tends to work in a lot of places, ranging from overperforming athletes suffering a sophmore jinx, to underachievers having a Cinderella story. In practice, these events simply reflect Regression Towards The Mean.
Over much longer periods of time, this oscillation tends to curve gradually upward. This is a result of Survivorship Bias. Things that don’t improve tend to stop existing after a while, so the only things that perpetuate in the universe tend to be things that make progress and improve in quality over time. The stock market is a crude example of this. The daily fluctuations tend to regress towards the mean, but the overall long term trend is one of gradual but inevitable growth.
Thus, even with Regression Towards The Mean, there is a bias towards progress that in the long run, entails optimism about the future. We are a part of life, and life grows ever forward. Sentient beings seek happiness and avoid suffering and act in ways that work to create a world state that fulfills our desires. Given, there is much that is outside of our control, but that there are things we can influence means that we can gradually, eventually, move towards the state of reality that we want to exist.
Even if by default we feel negative experiences more strongly than positive ones, our ability to take action allows us to change the ratio of positive to negative in favour of the positive. So the long term trend is towards good, even if the balance of things tends in the short run towards the average.
These dynamics mean that while the details may be unknowable, we can roughly predict the valence of the future, and as a heuristic, expecting things to be closer to average, with a slight bias towards better in the long run, tends to be a reliable prediction for most phenomena.