What this suffix does
-grounded forms compound adjectives with two connected meanings. The first is intellectual: well-grounded, firmly-grounded, soundly-grounded — describing a claim, argument, or position that is securely based in evidence, experience, or established knowledge. The second is psychological: a well-grounded person is one who is psychologically stable, secure in their sense of identity, and not easily destabilised by external events. Both uses share the root metaphor of having secure contact with the ground — the intellectual version means contact with reality and evidence; the psychological version means contact with one's own stable centre.