A Scorpio ascendant native is own rival as Mars is lord of the ascendant sign i.e. self as well as the 6th house of rivalry.
A positive attitude towards life will turn this rival into healthy competitor which means the person competes with self in getting better and continuouly tries to raise the bar. This helps such natives become much better and evolved versions of themselves.
A negative attitude on the other hand, turns the native to being own enemy thereby mostly losing virtues and good qualities over time. The negativity turns to toxic bitterness towards self and others.
The bhava (house) where ascendant lord Mars is placed is the source of this "rivalry" with self. With negative attitude towards life, this house becomes the limiting and challenging factor. Often this is where psychological healing is required.
For example, if Mars in Scorpio ascendant chart is placed in 11th house, the matters of that house will be the karanam (करणं) i.e. the instrument of competitive behaviour.
There's an independent and practically very effective principle in Jyotish classic Bhavarth Ratnakar that when a planet owns two signs and aspects (or placed in) one of those two signs, then it favours that sign much more than the other sign owned by it.
Taking the above sutra or principle forward, if Mars in Scorpio ascendant chart is placed in 3rd, 6th, 11th or 12th house, it aligns more with 6th house than ascendant sign as 6th house has Aries sign which happens to be Mars's mooltrikona (active) sign as well. Among these houses, 6th house is special in the sense Mars also aspects ascendant from 6th house.
When Mars is in 3rd house of sign Capricorn, it's not only in it's sign of exaltation but also gets attracted to such desires and goals (3rd house) that require direct competition, conflict and fights (6th house). By itself, this is not an ideal situation because Mars's aspect on own 6th house slightly favours rivals than self (planet aspecting own sign protects and favours it). As 6th house lord signifies ALL rivals (including self for Scorpio ascendant), the native often precipitates conflicts with others. Often it comes through false or misplaced bravado as Mars is significator of courage in the house of parakram i.e. valour. Should also watch out against family tension between self, younger sibling and father as Mars aspects 9th house.
When Mars is in 11th house, it creates either money/material related conflicts or challenges in native's relations with elder sibling, paternal uncle or son/daughter-in-law as relationship with them is signified by 11th house. This is also not a great placement for safety of native's spouse as Mars being 6th lord aspects 2nd house in this case, which happens to be 8th house from 7th house of life partner. 8th house is extremely sensitive house for everybody in terms of sudden, unexpected and dramatic experiences in life.
A Scorpio ascendant lord Mars when placed in 12th house triggers issues in life and marriage as a result of indulgence, enjoyments and vacations. This can also create imbalance in private moments in life whether it's carnal pleasures or spritual bliss as these experiences require maintaining delicate balance which is not exactly a strength of Mars as it's highly active planet as well as 6th house lord (and aspecting it too).
Remember, in all the above scenarios or even in ascendants other than Scorpio, whenever 6th house is stronger than the 7th, it will challenge martial harmony because 6th is 12th (physical reduction) from 7th house of relationship. If a Scorpio ascendant Mars aspects it's own 6th house, this situation is created. It's very relevant placement to relationship because Mars in this case is placed in Venus's mooltrikona sign of Venus. It would depend on placement of other planets notably Jupiter and Venus how well and strongly this challenge (to relationship) is outweighed.
In conclusion, it's important to note that our astrology chart indicates the quality and quantity of our Samskara (संस्कारं), our empirical subconscious mind that we brought from past existences. These samskara are responsible for the vrittis (वृत्ति) which are thought impulses in our mind driven by sensory perceptions. We can handle our challenges with better control on what we feed to our senses from outside and then scientifically control our thought impulses being repeatedly generated from within. Our ancients and sages have given us a plethora of scientific tools and techniques to exercise Raj yoga i.e. control over mental and emotional self.
