Not sure if you're into self-help books but there's a good one on validation called I Hear You by Michael Sorenson.
You can't really understand any other person, but you can identify and reflect the emotion they are trying to convey. "I can't sleep, I can't eat, I can't stop crying. I lost my entire herd of cattle in a barn fire." Do you understand that? I don't. I mean I can picture it but have I ever been a farmer whose livelihood is derived from intact living animals? No. So it's more like, "I'm sorry to hear that, you must be devastated." Or maybe you're not sorry because you were playing with matches nearby and you suspect that the farmer thinks it's your fault. So more like, "How horrible! I'm sure anyone would feel despondent after going through something like that."
A prerequisite to validation is empathy, having a basic emotional vocabulary and sensitivity that allows you to discern the key feeling the other person is trying to convey. You can say exactly the right thing for offering condolences to someone whose beefers are all well done and they're sad about it. But if they're angry, or happy, and you validate the sadness that you think they're experiencing because that's what YOU would feel, you did it wrong.
Plus you have to be in the right state of mind. If you're emotional, you can't really sense the other person's emotions, and the whole thing becomes all about you again. And that's why you GAL.
"What is best for my kids is best for me" Amor Fati Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712