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Project future trend of a stock with high positive autocorrelation
Auto-correlation is a statistical concept for measuring repeating patterns in series.  In stocks it is of particular interest as if future prices can be reliably guessed from past prices a lot of money could be made.   Note, even in cases where auto-correlations are high and persistent (near 1) there is still some possibility that the next time period would be down even if the previous period was up.  Now the important part here is that high and persistent auto-correlation also means once the price falls the next period the price is also more likely to fall! Once one period was down the next period is more likely to be down so the price does not need to go to infinity.  Instead, it generally would display up and down trends. Now, the key word above for investing is persistence. For stocks, auto-correlations are, at best, weakly persistent at reasonable time scales.  So, even if a stock was highly auto-correlated during a previous period it is tough to make consistent money off of trading on these past trending patterns.  This does not mean some people don't try...