Answer:
They can lead to unethical behavior.
Step-by-step explanation:
As the person which a conflict of interest will have to make a decision which influenciate his income, wealth or status.
The most common example is personal/sexual relationships between students or employees As there is a difference in rank the student or employee may accept as a refusal may lead to a bad grade or cease of contract respectively.
Another example is having a commercial relationship with a contractor/supplier while being in charge of the purchase department As will kept that supplier even when it is not preferrable for the enterprise.