Baldur's Gate 3: Proficiency bonus
All characters and monsters have a proficiency bonus, which is a kind of representation of their level applied to the areas in which they are competent. The bonus starts at +2 at level 1, and goes at +6 at level 20. It is applied to stats, save and attack rolls.
For example, a barbarian has proficiency in armor, common weapons, force and constitution, as well as certain skills. If he is asked to make a force roll to break down a door, his proficiency bonus applies. If asked to roll an intelligence to solve a puzzle, this bonus doesn't apply. In certain circumstances, this bonus can be multiplied or divided.
Once again, this will contribute to the specialization of the characters in your group, and it is better to choose to master fields related to your highest stats. The effect being cumulative, this will give you a better chance of performing difficult actions. For example, a very intelligent Magician who masters the History skill will receive massive bonuses.
