When trying to use $inc to increase the value of a property in Mongodb, the value remains unchanged.

let stats = {stress: -5, affection: 0, darkness: 0}

                  await Data.findOneAndUpdate({UserID: this.userID}, 
                        {
                            $inc: {
                                Stress: stats.stress,
                                Affection: stats.affection,
                                MentalDarkness: stats.darkness
                            }
                        }
                    )

I was expecting these stats to change accordingly and yes I did check that these variables returned what they were meant to. It works if I type the numbers instead of giving it a variable.