Needs editing, but am in a bit of a hurry, sorry
This short-term thinking has some side effects that affect the economy as a whole.
If you become CEO of a large company, it is actually quite easy to sustain a nice profit margin in the short term; just sack people at a faster rate than your turnover is dropping.
This has several effects for the long term; first, you hollow out your company to the point where all innovation stops and long-term performance is affected by lack of knowledge and skills; it could very well have been better to accept a short-term fall in profit margin.
Second, something which is conveniently forgotten in many mainstream economic theories: one company's employees are another company's customers, and contrary to popular belief, entrepreneurs don't create jobs, customers do. Through this self-reinforcing mechanism, short-term thinking can make the whole economy spiral the wrong way.