When I was a kid, my older brother and I got ahold of a Dungeons&Dragons 2nd edition guide. To us in the pre-internet age, it was a mystical book of wonders. We hacked up a play group and started imagining all sorts of adventures.
In case you haven't played D&D, its main weakness is the combat system. A Game Master (the one creating the adventures and rolling the dice) eventually finds it much easier to just throw enemies at his adventurers rather than think up elaborate puzzles that might stump them. We as kids had no clue about game design but we did eventually realize that any problem in an adventure can be solved by attacking it – if it can't be attacked we just don't want to play it. The combat works by rolling a d20, meaning a 20-sided die and seeing which number comes up. In essence, rolling a 1 means a critical miss, for example that the character fumbled and stabbed himself but rolling a 20 means scoring a critical hit, often dealing double, triple damage or outright killing a weaker enemy.
The chance to randomly select any outcome X out of a pool of Y outcomes is X/Y or in this case 1/20=5%. So, a player has 5% for critical miss, 5% for critical hit and 90% for just a regular hit or miss. In theory, this system is balanced but it doesn't account for wishful thinking. Now, the die doesn't remember what the previous rolls were but will tend to even distribution over a sufficiently long rolling interval. What this means is that a player could roll a die three times and legitimately get three 1s but if he just kept rolling he'd eventually get three 20s.
How do you think this affected the average adventurer? He loathed the critical miss mechanic. Despite the fact it was never a game-ending event, players would always throw a temper tantrum because they just couldn't handle that a die that could give them a juicy 20 humiliated them with a 1 instead. It felt rigged, unfair and a waste of time, even though it was just as likely as instantly killing an enemy, which could dramatically swing the battle. In the end, we had to soften up the critical miss mechanic until it was no longer relevant and afterwards just offered a free reroll every time 1 came up.
I didn't know about wishful thinking back then but now I realize that our brain is designed to slowly ramp up its expectations for the better. After all, we do want to do better as time goes on, right? But that means we slowly lose sight of the fact that critically bad events happen just as often as good ones but devastate us emotionally because we wishfully thought they'd never happen.
Applied to life, this small essay on rolling a die in D&D means that the majority of your days will be 2-19, meaning just average, with some slightly better than others, a small amount will be 20, a perfect day where everything goes your way and an equal amount will be 1s, meaning disastrous days where everything that can go wrong goes wrong. If you are stuck in wishful thinking mode and consider 20s as average, 1s will utterly destroy you emotionally, physically and financially to the point you'll feel their impact throughout decades. Since 1s will happen again and again and might even happen in a row through no fault of your own, it's crucial that you have a contingency for when they do occur and treat them like just another day in your adventure.
Your brain will typically ignore the perfect day but get fixated on the bad days unless you devise a set of redundant failsafes to help you bounce back. For example, you might lose your wallet, which might make you unable to access the ATM and take out a wad of cash for some time-sensitive purpose. So, the failsafe could be to have two wallets: the main one with cash and documents and the backup one taped to your armpit with some extra money. How about having another failsafe, a sock filled with some money and taped to the backside of your couch? As you think of all the worst-case scenarios, you can see them as fun challenges that can be overcome by basic planning so you never experience the devastating effect of probability.
As you grow older, you'll have more 1s and if you're not ready for them, you'll simply never recover mentally and their effects will just keep piling up. When I observe old people around me, I see in their faces the defeats of days past and the smoldering ruins of wishful thinking, where they imagined life will always be a perfect row of 20s. I believe the "winter is coming" tagline from Game of Thrones represents the somber realization of old age that youth is blissfully unaware of this accumulating probability that bad things will happen and utterly destroy our cozy, sun-bathed empire. The more 20s you had in your youth, the more 1s will come back to haunt you in your old age; the reverse holds true too, as a series of 1s in youth will make the person seriously examine the underlying causes, leading to a bountiful series of deeply cherished 20s.
By using math, we can see life as it truly is, a randomly distributed series of good, bad and average days that happened through no fault of our own, simply because it was their turn to happen. What we can do is adjust our attitude and prepare ourselves for the worst case scenario through redundant failsafes. Life is an array of experiences that all balance out in the end, so once you know the winter is coming, you can brace yourself and actually get to enjoy the challenge, knowing full well the summer is bound to come afterwards.