Num 12:2 So they said (Miriam and Aaron), “Has the Lord indeed spoken only through Moses? Has He not spoken through us also? and the Lord heard it”
Miriam and Aaron grumbled against Moses in regards to his marriage and perhaps in retaliation to him appointing 70 elders without their input. They retorted that Moses their younger brother had monopoly of Divine communications overstepping Aaron’s priest position and Miriam as a prophetess. Moses’ advancement was God’s Divine favor not his own self drive. Those who should have rejoiced in God’s doing in his life and their own found fault with God’s plan.
God calls believers to run the race set before them in their own assigned lanes looking unto Him the author and finisher of our faith. Aaron and Miriam had their own assigned lanes yet they chose to meddle in Moses’ lane. It is indeed foolish to focus and run in another’s lane. You have no right to frustrate others that have what you want that God did not plan for you. And if you are oppressed by others over God’s blessing and favor, the Lord hears and will fight for you.