For some people's Sun, the so called "sign" and the ascendant, the rising sign, are in the same sign.
The “sign”, the position of the Sun at birth, gives the direction and the way we express our will and our goals in life. The ascendant is the zodiacal sign ascending on the eastern horizon at the time and place of birth.
When those two important elements are in the same sign, we tend to believe that the sign's characteristics become stronger in the person's traits.
While this is sometimes true, in many cases we have to consider another essential element: the house where the Sun is located. By knowing the birth time and place, we can calculate the position of the 12 houses of the Zodiac.
When the Sun and the ascendant are in the same sign, the birth happened around sunrise. This “around” makes a difference.
If you were born before the sunrise, the Sun would be in the 1st house, the house of the personality, actually strengthening the traits of the sign.
On the other side, if you were born after the sunrise, the Sun would stay in the 12th house and the Sun sign qualities would be challenged by staying in the 12th house, which softens the ego represented by the Sun.
While it is straightforward to understand the Sun in the 1st house, the sun in the 12th house is less easy to interpret because the 12th house tends toward dissolving the ego in order to reach higher non-individual spiritual qualities.
As an example, while Sun in Aries with Aries ascendant reinforces the typical sign impulsiveness, passion and courage if the Sun is in the 1th house, when the Sun is in the 12th house the person will experience ambivalent Aries traits and a number of inner conflicts which might flow into spiritual achievements.
You can find out in which house the Sun is located by calculating the Astrological Birth Qualities report and selecting “Planets’ positions and aspects.” Then you'll see it in the “planets in houses” section.