The 90 degree angle takes as its reference the signs of the same modality, so there are natural squares between the cardinal signs, between the fixed signs and between the mutable signs.
Together with the opposition, it is considered a bad aspect, because the influences of one planet are in disharmony with the second, bringing excesses that in turn produce conflicts and difficulties.
Precisely because of that excess of energy, the disharmonious aspects are the most noticeable in any horoscope. They always require an adjustment from the native, even though we often have no control over it, since that energy is in excess.
The houses involved also take part in this disharmonious contact between the two, and reveal the sectors that, when mixed, become sources of learning and of annoyance.
The square is the aspect that brings the most growth, because beyond the problems that force us out of the comfort zone, its realisation happens in fourfold form.
There are squares that do not fall in signs of the same modality, when one of the planets or points is at the beginning of a sign and the other at the end of another sign.