Are you kidding!?! Have you ever met a Capricorn? They were probably a dark, gloomy, skeptical person; this is why Jupiter is exalted in Cancer, because it's the farthest place away from that sign, which was called it's "Fall," which for me is the main basis for the whole system of exaltations. Jupiter is an optimistic planet and one that tries to give opportunities, whereas Capricorn is the main sign of Saturn, the Lord of misfortune, depression, sickness and pessimism. Capricorn is the first sign to think "what's the catch?" When Jupiter is here, it's hard for people with this placement or Capricorn to think there's any hope at all, the challenge is that they must learn to have faith and look to the bright side, but keep their natural common sense. Exaltation is also a form of rulership.
Jupiter in Cancer is extremely good. These are very popular people who pretty much just have everything they need handed to them by others. I met a Sag girl with Jupiter here and Moon in Libra in 5th. She was so beautiful and people where nearly lining up to try to be her friend (or boyfriend)! This placement is good for fertility, Jupiter in Pisces might be the only one better. It's very good for judgement and common sense.
It's not hard to understand the exaltations when you consider the Fall; when a planet is in Fall, it's in the sign that tends to resist it:
Sun-Libra: Libra resist the urge to express individuality because they need partnership. Doesn't feel strong or totally certain in their direction or goal which might be susceptible to outside influence. Motives must be hidden/don't want to attract too much attention.
Moon-Scorpio: Moon is too unstable, the emotions can become self-destructive and compromising if not controlled. Can't comprehend sympathy well.
Mercury-Pisces: Pisces must believe that things will turn out the way they want it to turn out (ideal over actual), not the way it appears it will when negative. Questioning faith (or anything else) is blasphemous! "Words aren't real communication" Protect the secrets!
Mercury-Leo: Has made up the mind and the conclusion is definitely the right one!! (-rolls eyes-) Only sees things on the surface, seeks absolutes and exaggerates.
Mercury-Taurus: (seems a rough place for Mercury to be if not a Fall) Bad at abstract thought and academics, extremely stubborn, proud mind.
Venus-Virgo: (Weird, the only girl sign) Lacks self-esteem to realize what a great romantic partner they'd make, prefers solitude, prefers work to frilly emotions, finds extravagance laughable or enraging, paranoid about negative consequences of romance
Mars-Cancer: Worries too much about the consequences of rash action, direct action often fails, Cancer seeks safety and solitude, fears hostility and discord, but knows that conflict is inevitable (dillema).
Jupiter-Capricorn: Pessimism makes them ignore opportunities, "if there's bad, it's good, if it's all good, then it's all bad!" Obligations over freedom. Ethics vs. success. Fickleness makes them let go of good things too soon. Possibly some infertility.
Saturn-Aries: Aries is only the beginning and doesn't understand obstacles, when they arrive Aries just wants to keep fighting until they are defeated, rather than submit to or learn from them. Because they don't understand these things, the "real world" can depress them and put them into a long rut. Patience is a difficult lesson.
Uranus-Taurus: Taurus likes to keep things the same, shocking, radical and rebellious behavior is disruptive to harmony. Humanitarianism can disrupt monetary and social systems. Traditional perspective is favored and trusted over new insight.
Neptune-Aquarius: Aquarius needs cold, hard reason, it can't understand emotion or empathy and doesn't really care. There's no such thing as "psychic powers!" Emotional sensitivity is a vulnerability and a nuissance.
No one really is sure where Pluto's exaltation and Fall is, but I suspect Gemini is it's Fall because of how absent-minded and changeable they are. I can't see Pluto being in Fall in Leo or Aquarius, and the exaltation probably isn't Pisces since they've already got Venus.