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If predictions work is a matter of long term statistics and not a matter of single events.
If you bet for example at the number "6" when rolling the dice, then odds of 6.00 would be fair odds, because in the long run you would win as much as you lose (because of the winning probability of 1/6). As soon as any bookmaker would offer you odds of 6.5 you would win in the long run in case you accept these odds, even if you would lose more single bets than you won.
Concerning the match Brazil against Belgium, it is a very different thing if you take part in a tipster competition like this on on Steemit or if you bet against a bookmaker:
In the tipster competition you have to decide for a result even if the probability of every single possible result is lower than 50 %.
If you bet against a bookmaker you simply can leave out a game in case you think the offered odds are too low in relation to the winning probability.
You can find a rough idea about how to create own odds (which then you can compare with bookmaker odds) here.