"The rich man's wealth is his fortress, the ruin of the poor is his poverty"
This proverb is about security and a place to hide.
This is two Hebrew words qirya for city and az for strong. The idea is that the surplus of the rich person is a place to flee when things are going bad. It is their refuge and security. This idea of security against attack and problems is what controls the rest of the proverb.
This is the Hebrew word mehitta which means destruction, terror, or ruin. Solomon is saying that while the rich man has a place to hide from disaster and mistakes and oppression, the poor person is exposed. They have no such place. There is nothing backing them up when they make mistakes or when a powerful person seeks to dominate them or a disaster strikes.
There is an interesting implied idea here which is that the poor person should have been saving some measure of what they received, so that they would have some to bridge them over the tough spots. The clear implication is that you don't want to be poor so do something about it. Spending all that you have exposes you. It leaves you vulnerable to the issues of life. It leaves no room for mistakes. Get yourself out of this situation by saving a little bit every day.
This is the Hebrew word dal which means one who is low; one who has nothing. The image is between one who has surplus and one who does not. One who has planned ahead for the contingencies of life and one who has not.
One person feels secure (even though they may not be) and one feels exposed. Solomon is saying you have a choice as to which one you will be in this life, for the most part, unless injustice is at work.
This is the Hebrew word ris which means poverty. It has reference to those who have no surplus; those who live day to day and have nothing to give to others or to rely upon when things are difficult.
One of the lessons of life is that it is lived through generosity and the ability to give – having surplus time, energy, money, resources, etc. Therefore, if you are the person who is always taking and never have anything to contribute or give, then you are ruined.
Now if I can apply this in an interesting way that is the opposite of what one might expect. There are people in our society who, in a desire to have surplus money, give away all their time, energy, and other resources so that they are completely spent. They are deeply impoverished in time, energy, and resources and when others need these from them, they have none to give and they are ruined. This is what happens when parents give all their time and energy to money-making or lifestyle-acquiring and have nothing left for their children. This is what happens when the job consumes every minute, and we have no time for hobbies and friendships. This is what happens when we give all to impress others with our stuff and have no time for God. Our poverty of time, energy, and resources is our ruin, for we have no relationships except in the pursuit of money, prestige, or lifestyle.