Walk a mile in someone's shoes.
If you're good enough, they won't notice until yer at least a mile away and then you have their shoes! ARHARHAR! Ok, joking aside.
The idea is that after you walk a mile in someone's shoes, you have learned about them. As a metaphor, it's a pretty good one.
Pretty good ain't perfect.
Short of a Vulcan Mind Meld or becoming Rogue or Leech, you can never tell exactly what another person is thinking. You cannot know why they do something. You cannot comprehend their motives. You cannot grok them.
You can get close.
Close counts in horseshoes, grenades and nuclear war.
How close you can get depends on what you do. Just for example, let's take garbage collector. Pretty much everyone knows what a garbage man does. He picks up trash and hauls it off.
But what else? How about flat tires? How about sliding into the ditch on a clay road after a monsoon rain? How about getting in and out of the truck all day to get roll out cans that aren't by the road side? How about getting out, walking around back of the house to get a can for a person who physically can't get the cart to the curb? How about a jammed mechanism that has to be cleared before making the next pick up?
How about dealing with the refuse of thousands of people on a weekly basis? How about dealing, daily, with the stench of the garbage?
How about dealing with pissed off people who got their cart to the curb after the truck had gone by?
You may be very close to someone who has a garbage collection route. If so, you have a much better idea of what the garbageman goes through than the rest of us. Howsomeever, you don't, you can't know everything. You can't grok.
(Personally, I think using the excuse "Well, I'm married to - living with sibling/child/parent of - related to..." is a major cop-out. if you wish to offer their opinion, statement, observation, etc, do so. Just because you have a close relationship with that person doesn't mean you grok them.)
You may run a garbage route. If so, you very well may grok garbage collection. Only you can say that. However, you do not, can not know what another garbage man is going through. You do not know his entire life, his thoughts, dreams, desires, fantasies. You cannot be him. You can't grok him.
So the next time you decide to criticize someone for something they did, remember, You. Can. Not. Grok. Him.
You can second-guess, armchair quarterback and throw on a set of 20/20 Hindsight Glasses. You can criticize from your self-appointed post as the High and Mighty Arbiter of Garbage Collection and All Things Solid Waste. You can also be an Ass. You can also have both titles at the same time. Canya grok that? Maybe.
You can't grok another person.