"I'm a 5 kyu from the UK. I instantaneously I can tell those stones are light, however I can also instantaneously know the the reason why, probably because of how I learnt it from An Youngill Seonsu's detailed game reviews.

1-White's upper territory was already so solid it was extremely unlikely for black to invade. It doesn't make sense to complain about solidifying upper side territory that is already solid, since the net gain for white in solidness wouldn't be so great meaning it's easier to find a net benefit for black of equivalent or greater value to exchange it for.
2-If all of the black stones live, white has likely no possible centre influence from the upper side stones. However, of course, the black stones are weak. but even if white captures half of black's stones, it's still the case that the threat of white's possible influence has dropped from significant to not so significant, while white's solidness didn't increase much from solid to more solid.

We can conclude that light stones are light because _it doesn't matter that they're weak_, as the impact of each stone is so much that even if many of the stones are captured, the net benefit is still an overall positive. And this explanation comes to mind instantaneously to me.

Interestingly, I learnt the part about white being already solid so it doesn't mater if it get's more solid from something that had nothing to do with light stones. It was about deciding whether it's valuable to block or extend a side, I learnt the concept of an open skirt. I also learnt it overconcentrated stones. But those concepts apply well in an explanation for light stones.

This implies that light stones are a higher-level concept than those. Which means maybe a lot of the things you can't explain easily are hard to explain because they are higher-level concepts made up of lower-level concepts, so you have to consciously bring together all the lower level concepts into an explanation for the higher level concepts. So it's a lot like poetry.

He wants to approach on the lower side when black is already low on the left, of course white's going to push on D14 to make sure black cannot expand the left and turn the approach into a good move."