How did having a weak monarch lead to the French Revolution?

When you're a King of a country that has an enormous state debt (>400 million Francs), when your people live in poverty and the nobility in luxury, you need to be able to make bigdecisions to try to make things better. This is something Louis XVI couldn't do: make decisions. Something had to be done fast to make sure that money came in to lower the state debt (France was as good as bankrupt, and was later also declared as such) and to make sure the poor people got a better way of living. Louis got a lot of different advice from a lot of different political and social figures, but he never had an opinion of his own and couldn't make up his mind to do what he thought was right.

One day he decided to take the advice of one of his finance ministers and proposed to lower the taxes for the poor and to make to nobility and the members of the church pay taxes (they never had to pay taxes in their lives before). He changed his mind very fast when the nobility strongly objected against this proposal. He did not have the guts to push through and be a strong and firm king.

By this way of "reigning" he not only made enemies among the poor people (the lower class) who thought the King just didn't care about them at all because he didn't do anything to help them out, but also among the nobility and members of the church who were angry that the King had dared to propose that they would pay taxes (eventhough they were the richest!).