What is a conflict of interest?

What is a conflict of interest? Please, provide an example you have encountered or are aware of from your business or personal life.
Assume an employee is responsible for purchasing an apartment complex on behalf of his company. The employee owns stock in the management company that operates the apartment complex. The employee does not let his company know about his stock ownership and proceeds to make the purchase. Why does this example represent a conflict of interest?
Management of a cellular phone company learns a new technical advance will occur within the next year that will make the company’s current phones and related products obsolete. As a result, there is a strong chance the company will close. When financial statements appear for auditors, management does not reveal its knowledge of the new technology. In this case, what accounting and reporting concepts are involved?
What is the motivation for violating the generally accepted accounting principle of matching revenues and expenses? What is the result of committing this fraud?