Quote from harrytrader:
Easy:
Risk of ruin = 1-P[K]=1 - {1 - (q/p)^K0}/{1 - (q/p)^K}.
p is the probability of winning 1$ at each bet and q = (1-p) the probability of losing 1$ at each bet, K0 is your initial Capital and K the fortune you would like to reach.
Since you said
>Let's say I buy a stock at $11, which my analysis shows should >go to $13 in about two weeks. Instead, it drops down to $9 >about two days later.
the formula above applied just use K0/2 instead since it is 2$
And Since you said that "The cycle starts over" I suppose it means over and over again then q/p is even < 1/2 that is to say you don't even have a "fair game", a casino could be even more fair than you ... with yourself 
Prob faqs work in progress interrupted at the moment by other tasks on my site
http://www.econometric-wave.com/faqs/probability/home.html.html#Q_what_is_the_probability_of_ruin
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Quote from caplan8293:
Let's say I buy a stock at $11, which my analysis shows should go to $13 in about two weeks. Instead, it drops down to $9 about two days later.
I am disappointed and want to get out, but do not want to take a $2 loss, so I hold on to it, hoping for a rebound. A week later, it goes back up to $11, which would allow me to exit flat. Do I sell it? NO. Instead, I feel that if I hold on to it a little longer, it will still go up to $13.
So what happens? I hold on to it and it drops back down to $9. The cycle starts over.
What is wrong with me?
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