In certain group dynamics, you will notice three characters with different mannerisms, attitudes, and personalities that are easy to identify with — a character who is nice and gentle, a character who is mean and tough, and the character who is caught in between the two other characters.
Nice Character: This character is simply what they are — nice, polite, friendly, and helpful. They show everybody a great deal of respect and kindness, even to their worst enemies. They're the kind who never lose their temper nor resort to violence, although they do when pushed too far. Other variations would have them to be seen as naive and gullible due to seeing no reason to be justifiably angry with others and always believes there's some goodness in them, and often at times, they can appear to be too nice. They'll most definitely be the peacemaker when the mean and in-between characters get into fights, which can qualify them as The Heart. They can also serve as the Morality Pet for the mean character or even the inbetween character on their worst days. If they're the dumb one, they'll easily be a Kindhearted Simpleton. In a trio of siblings, they'll most likely be the youngest. They can be the Token Good Teammate if they're a part of a villainous trio or if the in-between character is more mean than nice. In a Freudian Trio, they're commonly either The McCoy or The Kirk.
Mean Character: The polar opposite of the Nice Character. Simply put, this character is rude, unfriendly, harsh, and abrasive. They're the one that the nice and the in-between character have trouble getting along with. The mean character will usually bully the nice character and will engage in fierce arguments with the in-between character. While they may turn out to be a Jerk with a Heart of Gold, they will put a heavy emphasis on "Jerk", and their heart of gold will appear on a few occasions. In a trio of heroes, they'll be a gritty and violent Anti-Hero who will show no mercy to anyone who gets in their way, or at least a Good Is Not Nice hero who genuinely does good, but is nevertheless rude and rough. They may be grouchy and cynical, always seeing the worst in everything and everyone. If they're the leader, expect them to be either strict and no-nonsense or bossy and egotistical. If not, they'll be The Lancer who will be the first to criticize The Hero's leadership or decision-makings. In a trio of siblings, they'll most likely be either the middle; rebellious and grumpy due to their placement of birth, or the eldest, if they resort to bullying their younger siblings. If the "mean" aspect goes too far, they can be the Token Evil Teammate. In a Freudian Trio, they're commonly either The McCoy or The Spock.
In-Between Character: This character isn't as well-mannered as the nice character as they have a few negative traits, but they aren't as abrasive and unpleasant as the mean character. They may be a Jerk with a Heart of Gold with a heavy emphasis on "Heart of Gold". If they're not a jerk, they will most likely have a Sugar-and-Ice Personality who can either be too aloof, quiet, or serious to be nice or mean. If they're indeed a Nice Guy, it won't be to a naively idealistic extreme, and not to the point of being a pushover. With the nice and mean character being respectively optimistic and pessimistic, the in-between character stands on the realistic side of things. If the nice and mean characters have a certain serious flaw such as being too naive or too rebellious and brash, the in-between character will often be the Only Sane Man trying to keep them in check. If they're the dumb one, this means that their niceness and meanness will vary from time to time due to their stupidity. They'll commonly have a close brotherly/sisterly relationship with the nice character and will have a rivalry with the mean character. In common ways, they will be The Leader or the mentor of the group who shows respect for their comrades while keeping the two in line in one way or another, mostly the mean one. For this case, the character will most likely be The Hero. In a trio of siblings, they're most likely to be either the middle, or the eldest; as they are lawful and charming as they care for their siblings, but can be judgemental. In a Freudian Trio, they're commonly either The Kirk or The Spock.
Darker versions of this trope can qualify. For example, if there is a trio of villains or jerks, there will be one who is nicer or more innocent than the other two and the other villain/jerk who is more villainous and meaner than the other two.
If this trope applies to three female characters, they'll typically be Town Girls too, with the nice one as the Girly Girl (unless she is an Alpha B*tch), the mean one as the Tomboy (Unless the Girly Girl is mean, then she’ll likely be in-between) and the in-between one as neither.
If there are 6 characters in a group, the dynamic will come in 3 pairs, meaning that there will be a nice pair, a mean pair, and an in-between pair.
Note that this group dynamic can be a unique way to establish moments of how each character acts and what defines them. This is a snippet in the Power Trio explaining the basic makeup of trios — "Trait 1, Trait-opposite-of-Trait-1, Trait-Between-the-Two."
Compare The Good, the Bad, and the Evil, a scenario in which the trio gets into conflict with each other.
