I have read on vaious places: Pluto-Mercury stressful aspects (Conjunction- Opposition and maybe square)And Pluto- Sun harsh aspects.
But it depends on what area etc. For ex a saturnian person having saturn in aspect to sun and/or mercury would be interesed in developing itself=saturn=crystalisation.
A saturn-mercury persun would for ex maybe be harsh in his way of speaking and interactions with friends etc. But when he gets home he will think over it, see his own faults and wanna become better, but it takes A LOT of effort! (virgo in this mix is important aswell)
Sun-Pluto-Mercury: Sun is the identity, the ego, the life force. Pluto will wanna delve deep into all that sun matters. The person will be extremely interested in personal development, psychology. He/she would wanna know why he/she acts like this or that. Thinks like this or that, and wanna transfor his/her ways. He/she will be very interested in going deep inside his/her own soul, mind, be his him/herselves own psychoanalyst!
Wanna know his/her own true essense etc, thise are what comes to my mind anyway^^
Searching for its true identity.
He/she will be very fascinated about both him/herselves psychology and other peoples aswell. As this energy is not used only on oneselve,, its used on understanding other people aswell. Thats why I got into astrology. And why I'm so fascinated by serialkillers and the tv-series "criminal minds", but thise past year I can not stomach violent tv-shows or reading about violence and serial killers anymore. I have instead turned more to normal psychology regarding relationships, behavioural patterns etc.
How good the person are at it, well its a process, a lifeling process. One will have its ups and downs and transits and other factors will play a big role.
Know that, they are truly motivated and do wanna "master" it, to transform it, and they know, its not easy...
I have Pluto in 3rd, Oppo Sun-merc in 9th.
Mercury is also sesquisquare Saturn.
And I have a virgo asc.
All above is my reflections that I have felt, since I was around 6-7 years old.
People have "criticizing" voices in there heads,. Both good n bad critizicers with different roles.
I have had a clear "psychoanalyst" voice in my head since I was 12 years old haha
I started to "self analyse" my feelings and thoughts when I was about 12 years old, I remember what and where and the exact thought as clear as it was yesterday.
It does not mean I'm super good at it. It means that part of me has always been very awake. I know of friends who never likes to analyze themselves. They wanna live in a "happy denying bubble". That way they never develop imo but they are happy so what do I know?