Poland-Lithuania was one of the great powers of continental Europe after the treaty of Lublin in 1569. But after the rise of Russia as a great power after its defeat of the Swedish Empire it became gradually weakened and a protectorate of Russia. This led to civil war in Poland and its eventual complete annexation by Austria, Prussia and Russia in a series of three partitions in the second half of the 1700s.
After the first partition in 1772, King Poniatowski of Poland attempted to strengthen Poland militarily and civilly in a series of reforms culminating in the May Constitution of 1791 adopted by the Great Sejm and which would have turned Poland into a Constitutional Monarchy.
However, a group of Polish nobleman, angered by the removal of their privileges, formed the Targowica Confederation in St. Petersburg with the backing of Empress Catherine II. They criticised
The contagion of democratic ideas
And
The Parliament ... has broken all fundamental laws, swept away all liberties of the gentry, and on the 3rd May 1791 turned it into a revolution and a conspiracy.
This led to the Polish-Russian War of 1792. Neither side scored a decisive victory and eventually King Poniatowski sought a diplomatic solution and was forced to join the confederacy at the insistance of the Russian Empire. This led to the second partition of Poland reducing its size to a third of its former size and which was ratified by a coerced sejm on 23 November 1793. Two years later, Polish sovereignty was entirely extinguished when the region was annexed by Austria, Prussia and Russia.
This came mostly as a surprise to members of the confederacy who had only wished to see the status quo restored. According to Wikipedia, Targowiczanin meas traitor in Polish even today.
Q. Why did the Targowica Confederation not forsee the eventual outcome of their armed resistance to the democratic reforms instituted by King Poniatowski?