A monster's personality is made up of four variables:
"Bravery", "Caring", "Prudence" and "Motivation".
These values fluctuate depending on the orders
you give in combat:

CHARGE:   Bravery up, Prudence slightly down
MIXED:    Prudence up, Caring slightly down
CAUTIOUS: Caring up, Bravery slightly down

Motivation increases when you use any strategy except
COMMAND, and decreases when you use COMMAND.
Running away from combat decreases all your monsters'
Bravery and Motivation considerably.

Personality variables only change when you explicitly
choose a strategy for each monster during combat.
If you skip this step by choosing FIGHT, or if you use
an item, none of your monsters' personalities change.

The higher a monster's level, the more slowly its
personality changes (i.e. fewer points are added or
subtracted to the variables each time you select a
strategy)

A monster's personality type is determined by which
of the first three characteristics are high, low, and
average, as follows:

Type       Br Ca Pr
-------------------
HOTBLOOD   Hi Hi Hi
DARING     Hi Hi Av
DAREDEVIL  Hi Hi Lo
LONE WOLF  Hi Av Hi
VAIN       Hi Av Av
EZ GOING   Hi Av Lo
SMUG       Hi Lo Hi
SNOBBY     Hi Lo Av
RECKLESS   Hi Lo Lo
COOL/CALM  Av Hi Hi
WHIMSY     Av Hi Av
NOSY       Av Hi Lo
WHIZ KID   Av Av Hi
ORDINARY   Av Av Av
HASTY      Av Av Lo
STUBBORN   Av Lo Hi
REBEL      Av Lo Av
SPOILED    Av Lo Lo
HUMANE     Lo Hi Hi
UNCERTAIN  Lo Hi Av
CARELESS   Lo Hi Lo
SHREWED    Lo Av Hi
CAREFREE   Lo Av Av
GULLIBLE   Lo Av Lo
SLY        Lo Lo Hi
COWARD     Lo Lo Av
LAZY       Lo Lo Lo

Personality traits can be observed in slightly more
detail by talking to your monster in the room west
of the registration desk at the arena.  The things
your monsters say there are determined by all four
of their characteristics.  Note that this is the only
way to check "Motivation".

The first three personality traits determine whether
or not a monster will obey a command.  In general,
monsters prefer to obey commands that suit their
strongest characteristic: Brave monsters prefer CHARGE,
caring ones CAUTIOUS and prudent ones MIXED.  Note that
a monster with low WLD (wildness) will usually obey any
command, and a monster with extremely high WLD won't
obey even a command suited to its personality.

"Motivation" affects the ease of raising the other three
personality traits.  High "Motivation" causes traits to
increase more rapidly and decrease more slowly.

Finally, each personality trait occasionally has a
special effect in combat (accompanied by a message).
The higher the trait, the more often the effect occurs.

Bravery:    Critical hit with a physical attack
Caring:     Use a healing skill without spending MP
Prudence:   Status attack ignores the victim's resistance
Motivation: 50% additional damage with any attack

There are apparently the following special effects
associated with extremely low personality traits,
but I've never seen any of them occur while playing.

Low Bravery:    Additional 50% damage cut when DEFending
Low Caring:     Use an ally as a shield
Low Prudence:   Automatically counterattack
Low Motivation: Automatically evade an attack