In 11:28-29, after Moshe gathers 70 Elders of Israel leaving two behind, we find the two begin prophesying in the camp. Somebody (Gershom perhaps) sees and runs to tell Moshe. Yehoshua gets upset and asks permission to kill them off. Moshe responds - are you jealous for me? What would I give to have the whole nation as prophets of Hashem....
The natural reaction a person has to the success of other people is jealousy and an attempt to denigrate that person. The success of others is often perceived as a threat to you. To ensure your own success, you feel you have to knock down other people.
Moshe said that that is not the way. We must strive to be successful, but we should also be happy about the success of others. We should strive for their success, and we should encourage them to succeed. Their success should be seen as independent from yours. You can both be successful.