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In general, dreams arent something that could really be that reflecting out on what would happen in the future but there are indeed instances that
dreams do connect out with reality and there's no way about proving it out on how it did happen.
And if you ask how the dream came about or reflects a reality,
I guess it's just a coincidence and what is dreamed of is a manifestation of our subconscious about the activity being performed.
There is no valid evidence of a dream that always comes true.
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As you rightly point out, dreams are part of our subconscious, and thinking about gambling before bed can influence dream content without necessarily having any predictive power.
You seem to have explained about dreams and their relationship to gambling clearly and also based on scientific things.
Anecdotal experiences can indeed be the trigger for a dream that can be quite unique, dreaming about lottery numbers,
about signs that produce special numbers that will come out, and the like.
Our subconscious will process all anecdotal experiences into an image in a dream, this will be an illusion that looks real, but will not be proven.
So anyone who believes in a dream completely, it cannot be true.
Dreams can be a motivation to achieve what has been dreamed of and can come true in the future.