(in order of priority)
1. Beware David Hume's black swan.
No amount of observations of white swans can allow the inference that all swans are white, but the observation of a single black swan is sufficient to refute that conclusion.
Chickens pay the ultimate price by haemorrhaging like elephants.
2. Heed Solon's warning: It ain't over till it's over.
3. Learn from Odysseus who stuffed wax in his ears in the Sea of the Sirens:
I am not intelligent enough, nor strong enough, to fight my emotions.
4. Do not get married to yourself. Change your ideas and opinions as often as is necessary.
(In a parallel, Arthur Rubinstein was known as a pianist who changed his musical ideas and thoughts on a whim, much like George Soros and his investment principles.)
5. Children only learn from their own mistakes, no possible warning by others can prevent them from touching the hot stove. Likewise, book knowledge never lasts compared to life's (bitter)experience.
6. Yiddish saying: If I am forced to eat pork, it better be of the best kind.
7. Maths is a way of thinking, (much) more than a way of computing.
8. Your life expectancy increases each year you get older. If national life expectancy is 75, and you are 74, you are NOT LIKELY to die the next year. Remember that 50% of the population have lower than national life expectancy.
Other similar sayings: 50% of the population has lower than average IQ.
If you are not doing more than the average, you are pulling the average down.
9. Survivorship bias:
Imagine 1,000,000 analysts (or monkeys) making completely random predictions on 2 outcomes (market go up/market go down). 1 epoch (whatever length of time you may choose to define) later, only 500,000 analysts get their predictions correct.
Another epoch later, 250 000 analysts remain standing. After 15 epochs, there are still at least 30 analysts (1mil/ 2^15) surviving with 100% records. They are the fools of randomness we worship as Gurus.
10. Gurus usually develop the unfortunate habit of writing books about their random success.