"Ruin" is just a way of stating that there is something (at least one thing, often many) that a person feels is destroying their serenity, their happiness, etc.
You could also use a word like "lodestone", where it infers all of your attention (or a majority of it) goes to that issue or person and it overwhelms you.
I've heard many people use similar terminology outside of Scientology. I disagree strongly with the process of sticking someone in a "ruin" as a sales technique. I find it abusive and unethical. However, if a person has such an issue and it's sitting right below the surface all the time, you could be doing them a favor by getting them to confront it and do something about it. It depends on how much "ego strength" the person has, and I don't believe that modern scientologists or many others have the sensitivity or tools to be aware of this with any degree of accuracy.
In the days of Science of Survival (51), the means of determining this was in the back of that book, I can't remember the name of the chart. However, right next to the "tone level" was listed the type of techniques that should be used to build the person's capability of confronting "charge" up. I believe this is a valid concept, even if much of Hubbard's explanation and theory were flawed.
If a person who is on the edge is pushed hard to dive into something extremely touchy or "charged", I do believe you can do damage to the person. "Ruin-finding" could do this, and shouldn't be used by people, I don't think, except in clinical environments, where the clinician is trained to recognize borderline personality disorder and other such indicators of low "ego-strength".
There is no need to hard-sell real help.