Stability in business
Business' want stability and profits, sometimes companies can put long term stability at risk due to the pressure on surviving in business. This is not necessarily business' fault just how economics works, it's similar to athletes who can put their long term health at risk by taking certain drugs to improve short term goals.

Retail and investment banks
Combining the retail banks and the investment banks adds greater risk to the whole economy if you potentially go under as everyone loses their money, the benefits for the company is using the money from the retail banks in the investment banks what is more profitable.

Any company that decide to combine both sides of the bank can make more profit and make better offers to customers. Even though decisions like these can make you more unstable in the long run, any company that decides not to combine both sides of the bank can be less profitable and is more likely to go out of business, so you will more likely see companies putting their stability at risk to survive in the short term.

Marxism and stability
Marx thought there was an inherit unsuitability running through the history of capitalism. One of his ideas was if bosses got their way and paid their workers less and less, then those workers would have less and less to buy what the bosses are selling, driving a decline in the economy. But a squeeze in workers earning doesn't always mean there will be a decline in the economy.

In the past workers got the money and bought the products as well as making the product, so a decline in wages meant a decline in demand. But when bosses have a larger share of the profits to spend they have more power on demand, so they can sustain the demand.

Housing
This effect can be seen in certain saturated housing markets, where the landlord is the boss and the tenant as the worker. 
So even when less people have buying power to own their own home, there are enough landlords to own the majority of the homes in the area and they are the ones who keep the housing market prompt up. And if home building is slow enough any new homes that are build will be consumed by these landlords.

2 flaws of capitalism
A barometer for any economic system's success is it's ability to increase happiness. Capitalism has been a successful system at increasing happiness, though it does come with flaws in it's purest form such as allowing monopolies and allowing companies to stifle competition. These types of problems are part of the two biggest problems in the most purest forms of capitalism.

Only thinking of your own interests

This is normally a benefit thinking of your own interests as it improves competition, but sometimes you are not the only person at risk from the actions you're taking. Imagine we allow companies to freely buy land, build a nuclear power station and have their own safety regulations. As a owner of the power station your risk is the profits of the power station, not of people who live around the power station. As you can see risk isn't just on the owner of the company and the people who buy the products.

Elk need larger antlers than their peers when fighting to find a mate, but the larger antlers actually make it harder to run away from predators, it would be in all their own interest if they all had smaller antlers as it doesn't matter how big the antlers are but how big they are to your nearest competitor.
This is the same case for certain companies when advertising, you have to spend more than your competitor on advertising but this hurts both your companies having to spend so much money on advertising, it would be in both your own interests to stop advertising in certain cases.

People not knowing what's in their best interest
There are two main reasons people make decisions that are not in their interest's. 

1. Lack of knowledge can make it hard to compare two products or to make a decision on if a product is right for you harder. To know if you are getting the best and appropriate healthcare can be difficult when you don't really know how to even compare what is a better healthcare plan. You may believe you have all the relevant information to make a decision but even then you can't be sure and it's in the companies interest to suppress information that would be harmful to it's profits.
2. We are not 100% rational beings, our brain's are wired up to want and act certain ways what can be detrimental for us and against our own interests, such as wanting to loose weight but having craving to eat more, wanting to stop smoking, etc. capitalism can play on our craving and the quirks of how our brain is wired up and actually make us more unhappy in the long run.