However, sometimes not feeding into one's jealousy is extremely difficult and can be arduous emotional work. The Pele Yoetz writes that the best way to save oneself from falling into the rut of envy or heal oneself from being envious is to strengthen his Emunah. He quotes the words from Chazal: אין אדם נוגע במה שמוכן לחברו One cannot touch that which was preordained for his friend. One cannot in any way take even a tiny part of what was destined for his friend.
A person must believe that even if he would be the only person in the world, nothing would be different. He would still have the exact same portion as he does now; his life would be all the same. Nothing else would be available to him, regardless of whether there were other people with whom he apparently has to share that which is available to him. This is exactly what was destined on High for this person. Whatever has been granted to him is what's important for him in order to fulfill his tafkid in this world. Anything else that hasn't been granted to him isn't only unnecessary, but not good for him.
The opposite also applies. Even if there would be thousands of merchants dealing with the exact thing he is, it would not take away a grain from him. For what he has - his successes as well as what seem to him as his losses - have nothing to do with what anyone else has. Every person is granted his needs, no matter what is going on in anyone else's life. (פלא יועץ)