Validating comes from empathy, which is why LISTENING is soooo important.
Empathy being the understanding of another's feelings. The beauty being, we all have the same feelings. We know what it's like to be sad, happy, angry, frustrated, worried, etc...
Someone can say to me, there was this one time I lost my favorite marble in a well... Geeze, I've never lost a marble down a well... so how can I empathize... but I HAVE lost something that I could not get back and I know the feelings associated with that, so I can legitimately say:
"I know how you feel"
When we're empathizing with someone with whom there is friction, it is tough... if my W would say to me,
"You never helped around the house..."
I would be thinking, what have you been smoking, woman... so that's when I have to step out of my box, drop my truth of the sitch, and think to myself... "That is how SHE feels. I may not agree, but for whatever reason, she believes it... and I guess I could have done a little more or let her know I appreciated all her effort..."
So in that case, I could simply validate and say:
"I understand how you could feel that way..."
It's MOST difficult to empathize and validate when there's some sticking point... so that's where we need to utilize 5 second rules and deep breathing... to keep us calm, allow us to think for a moment, and then we can respond...