The background of D'Alembert
The D’Alembert strategy was created by a French mathematician and physician by the name Jean Le Rond D’Alembert. He based the strategy off on Martingale and developed it with the intentions of neutralizing the downsides that the Martingale roulette strategy has.
Jean Le Rond lived in the 18th century and had a theory that an outcome with a 50% chance of occurring would always balance itself out in the end. He proposed that the chance of outcome A occurring would increase if outcome B had happened many times in a row. An example of this would be that if a red number had been hit many times in a row at the roulette table, the chance of a black number occurring would be increased so that they would balance themselves out in the end, resulting in both black and red having occurred equally many times.
Nowadays we know that this is incorrect as the chance for a certain outcome to happen in roulette is always the same no matter if red have occurred 20 times in a row.