INFPs in short:

Full of enthusiasms and loyalties, but seldom talk of these until
they know you well.  Care about learning, ideas, language, and
independent projects of their own.  Tend to undertake too much,
then somehow get it done.  Friendly, but often too absorbed in what
they are doing to be sociable.  Little concerned with possessions
or physical surroundings.

About 1% of the population.

Details about INFPs:

INFPs present a calm, pleasant face to the world and are seen as
reticent and even shy.  Although they demonstrate a cool reserve
toward others, inside they are anything but distant.  They have a
capacity for caring which is not always found in other types.  They
care deeply - indeed passionately - about a few special persons or
cause.  One word that captures this type is 'idealistic'.  At
times, this characteristic leaves them feeling isolated, especially
since INFPs are found in only 1 percent of the general population.

INFPs have a profound sense of honor derived from internal values.
The INFP is the Prince or Princess of mythology, the King's
champion, Defender of the Faith, and guardian of the castle.  Sir
Galahad and Joan of Arc are male and female prototypes of an INFP.
To understand INFPs their cause must be understood, for they are
willing to make unusual sacrifices for someone or something
believed in.

INFPs seek unity in their lives, unity of body and mind, emotions
and intellect.  They often have a subtle tragic motif running
through their lives, but others seldom detect this inner minor key.
The deep commitment of INFPs to the positive and the good causes
them to be alert to the negative and the evil, which can take the
form of a fascination with the profane.  Thus INFPs may live a
paradox, drawn toward purity and unity but looking over the
shoulder toward the sullied and desecrated.  When INFPs believe
that they have yielded to an impure temptation, they may be given
to acts of self-sacrifice in atonement.  The atonement, however, is
within the INFP, who does not feel compelled to make public the
issue.

INFPs prefer the valuing process over the purely logical.  They
respond to the beautiful versus the ugly, the good versus the bad,
and the moral versus the immoral.  Impressions are gained in a
fluid, global, diffused way.  Metaphors and similes come naturally
but may be strained.

INFPs have a gift of interpreting symbols, as well as creating
them, and thus often write in lyric fashion.  They may demonstrate
a tendency to take deliberate liberties with logic.  Unlike the NT,
they see logic as something optional.

INFPs also may, at times, assume an unwarranted familiarity with a
domain, because their global, impressionistic way of dealing with
reality may have failed to register a sufficient number of details
for mastery.  INFPs may have difficulty thinking in terms of a
conditional framework; they see things as either real or fancied,
and are impatient with the hypothetical.

At work, INFPs are adaptable, welcome new ideas and new
information, are well aware of people and their feelings, and
relate well to most, albeit with some psychological distance.
INFPs dislike telephone interruptions and work well alone, as well
as with others.  They are patient with complicated situations, but
impatient with routine details.  They can make errors of fact, but
seldom of values.  Their career choices may be toward the ministry,
missionary work, college teaching, psychiatry, architecture,
psychology - and away from business.

They seem willing and usually are able to apply themselves
scholastically to gain the necessary training for professional
work, often doing better in college than in high school.  They have
a natural interest in scholarly activities and demonstrate, as do
other NFs, a remarkable facility for languages.  Often they hear a
calling to go forth into the world to help others; they seem
willing to make the necessary personal sacrifices involved in
responding to that call, even if it means asking others to do
likewise.

INFPs can make outstanding novelists and character actors, for they
able to efface their own personalities in their portrayal of a
character in a way other types cannot.

As mates, INFPs have a deep commitment to their pledges.  They like
to live in harmony and may go to great lengths to avoid constant
conflict.  They are sensitive to the feelings of others and enjoy
pleasing those they care for.  They may find it difficult to
reconcile a romantic, idealized concept of conjugal life with the
realities of everyday living with another person.

At times, INFPs may seem fearful of exuberant attainment, afraid
that current advances may have to be paid for with later
sacrifices.  The devil is sure to get his due if the INFP
experiences too freely of success, or beauty, or health, or wealth,
or knowledge.  And thus, INFPs guard against giving way to relaxing
in the happiness of mating.  They may have difficulty in expressing
affection directly, but communicate interest and affection
indirectly.

For INFPs, their home is their castle.  As parents, they are fierce
in protection of their home and family and are devoted to the
welfare of family members.  They have a strong capacity for
devotion, sympathy, and adaptability in their relationships, and
thus are easy to live with.  They are loyal to their family and,
although they may dream of greener pastures, they soon locate the
nettles.  The almost preconscious conviction that pleasure must be
paid for with pain can cause a sense of uneasiness in the family
system of an INFP, who may transmit an air of being ever-vigilant
against invasion.

In the routine rituals of daily living, INFPs tend to be compliant
and may even prefer having decisions made on their behalf - until
their value system is violated!  Then INFPs dig in their heels and
will not budge from ideals.  Life with an INFP will go gently along
for long periods, until an ideal is struck and violated.  Then an
INFP will resist and insist.