TenYears,
The Holy Spirit is the spirit of Truth. We may not know what truth is, but we know what it isn't. There is something in your own conscience that resonates and confirms when you "know" something is true. I think thats what it means when it says the Holy Spirit bears witness. This awareness, or Holy Spirit, confirms for you what you know is truth or a lie.
To grieve the Holy Spirit is to ignore the truth and go along with something deceitful or lying, purposely.
This is why so many struggle with conscience by staying in the org "for family" when they know it is all a lie. It prevents them from being true to themselves. However, some have been able to resolve it because they are stalling for time or making subtle influences in order to rescue their loved ones. They feel they must stay in ( even against their conscience) in order to eventually reach their loved ones.
It seems some are destroyed in the process of holding on. Sometimes their loved ones will never change. Grieving the Holy Spirit slowly destroys your soul.