(Gambling strategies, wagering schemes, roulette systems, betting methods.)
You and your wife decide you want to have nine children. Pretend for the purpose of this example that the number of male births equals the number of female births and no genetic predispositions exist. You want to have all boys. What are the odds of having nine boys and no girls? Astronomical. That's sequential probability.
Now your wife has had eight boys. She finds out that she's pregnant. What are the odds that it will be a boy? 50:50, right? This is absolute probability.