Benefits of having an enemy outweighs the costs. Moreover, you will suffer if you do not have a real oppponent because a strong opponent makes you tougher, bolder, stronger and wiser. Your oppponent makes you challenge your limits and makes you alert to threats.
The real harm is not made by your opponent because you are expecting the possible attacks/threats and you are presumably well prepared for them. However, the real damages result from the ones you do not expect: Your seemingly friends; Voltaire was definetly right in his pray: “Lord, protect me from my friends; I can take care of my enemies“. And the damage from your friends is more psychological than material.
My personal manifestation:
I have always thanked to all who tried to willingly and consciously deceive or hurt me. I do not curse them. Actually, they have not worked against me, on the contrary, they worked for me. They are my best allies. Their cruel intentions trained my receptors to seize the hidden agendas easily, accurately and promptly more than ever. I think that if I want to be a better manager, I have to distinguish the good from bad, honest from hypocrite, and real from false. I would not learn to distinguish them unless I have been deceived or tried to be deceived by my opponents. And I have always protected my self respect and self image by not applying any immoral tactics as my antagonists did. I believe that the key point is this. You should resist not to be pulled to the immoral area. The merit is not to be right but to sustain the legitimacy.
Moral of the story: Competition is great. Opponents are greater. Challenged by an opponent, you leave your comfort zone. You practice, think and develop strategies. If your competitor is as clever as you, than you are luckier because you develop faster and better. You need to thank to your enemies rather than cursing them.
Song of Desree (You Gotta Be) makes you feel like you are stronger :