Friendship with the enemy

Friendship is always unpredictable. Everybody has friends but we can't explain this phenomenon. This is the case when there is no theory, there is only practice.
Sometimes our friends turn into our enemies and enemies turn into our friends. It may sound strange but it is really so.
Sometimes enemies become friends because people find similar interests and because they start to spend a lot of time together.
Enemies hate each other but they also respect each other. Some people even say that our friends are our potential enemies.
So is friendship with enemy possible?
There are a lot of examples that prove that friendship between enemies is really possible. According to psychologists enemies are people who have mutual intentions. A person understands that his/her enemy is the only person who may either achieve the same goals as a person or destroy his/her personal plans. Competition turns people into enemies.
But when the common enemy appears, people unite against him/her. At first hater unites them, but then they understand that they have a lot in common and that they have even the mutual respect. And as a result they become friends and sometimes their friendship is very strong. Such friends always tell truth to each other. And such friend is always ready to tell you about your faults and minuses. He /she will tell you that your actions in this or that situation are awful; your friend may also tell that this skirt doesn't suit you, and he/she will tell you when it is enough to eat and it is a time to go to the gym.