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Not sometimes, but all the time the game of football is unpredictable and the same as all other gambling games, most people thought Argentina will have a slide win in the match against Suadi Arabia but the outcome of the match was different and most gamblers got the tickets destroyed with just that one game.
Similarly, the game between Cameroon vs Brazil also is one game that got most football speculators off guard because most people gave Brazil straight winning in their ticket.
Football matches always seem more predictable, but they are often open to surprises. I want to say that I agree with you on this matter. If only the favorite teams win, the non-favourite teams hate to live and stop competing. :)
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I'm sure there are thousands of people who bet on the Argentina vs Saudi Arabia match and lost their money. I think it's perfectly normal to lose a bet on this game and I have to admit that I lost my bet on this game too, but I didn't put all of my money on this bet because I knew the problems that such a risk could bring.