Bitterness is a root that grows wide. It will grow deep as well, if it can but it does not need a lot of soil. Any little reason will let bitterness take root. You can grow bitter because you were truly treated poorly by your parents, or your brother was a better athlete, or your sister has a better voice, or a fellow employee got the promotion, or someone younger than you tried to teach you something, or a sister in the church who looked at you with a funny look on her face that you took to be a haughty glance at you. It turns out she was squinting at the clock wondering if she had remembered to set the automatic timer for the Sunday roast.
She did, in fact, remember to set the timer, and the roast cooked for several hours and grew juicy and tender and was consumed by all with great joy for a Sunday feast.
And you nursed that little squint for five years and your heart grew hard and sinewy at her blessings and you were consumed with envy culminating in misery and sorrow and Sundays were never a feast.
Maybe that is a bit of an exaggeration but it can and does happen. Envy and bitterness do not need much room to grow. So, don’t let them. Think of others more highly than you think of yourself. Rejoice in the bounty of your brothers and sisters in your own family and in the family of God.