The Estates General may well have been Louis XVI's greatest mistake! At least, it was his greatest mistake with regards to his career as monarch. For the rest of France-- nobility excluded-- it was a great decision.
The Estates General of 1789 was called for by King Louis XVI to address the economic state of the nation of France. His grandfather and predecessor, Louis XV, had run the government into near bankruptcy with involvement in the American Revolution. What's more, several years of bad weather had put a real stress on the crops of France, and the nation was now experiencing a food shortage. This drove up the prices of food, with the effect of angering a great number of people. The Bread Riots were primarily composed of people who contributed to the production of food yet could not afford to purchase even the most basic of foods-- bread.
The dire economic circumstances were exacerbating already underlying tensions to do with the weakened feudal regime. Peasants, who worked the land with little agency in their lives, were keenly aware of their situation. Influenced by Enlightenment philosophy, the increasingly literate commoners of France wanted change. It was at the Estates General that they took control of the situation and essentially told the nobility (including the King) that they would institute reform with or without their help.
The Third Estate (the peasantry) outnumbered the nobility two-to-one. Though the role of the First Estate (the clergy) had previously been to maintain that the feudal system of the Three Estates was a God-given command, many of them sided with the Third Estate during the early days of the Estates General. When the King realized that he would be overpowered by the Third Estate and associated clergy if he did not choose to cooperate, he urged the remaining nobles and clergy to "give in." With this, the Three Estates became the National Constituent Assembly, and King Louis XVI begrudgingly took a back seat in implementing the desired reform.
If he had never called for the meeting of the Estates General, Louis XVI might have remained King for much longer.