To understand the expression, to understand its origin, you must first know that it is a figurative expression. You imagine that you are attracted to something that shines because you think it is gold. From afar, you see something that shines. The sun sends its light on an object and this object returns light, it reflects light, so it shines. And you are attracted to this object. You say: "It looks like gold". And when you get closer, looking more closely, you realize that it is not gold, so it is not the precious material that you expected.
So, with this image in mind, you can understand that the expression "all that glitters is not gold" means that you should not trust appearances. Here, it is not because an object shines that it is gold. This is true for many other things. Things are not always what they seem to be. It is not because something looks good that it is germany whatsapp number data necessarily the case. Just as it is not because something shines that it is gold. So "all that glitters is not gold" means be careful, you should not only trust appearances, only trust what you see, since things are not always what they seem to be.
I think this is relatively clear, but it is always interesting to take some examples to intensify your understanding of the expression.
First example, you saw a small ad for a house, you want to buy a house. You say, after seeing a great ad in a newspaper: "This ad for a house seems a little too perfect to me. All that glitters is not gold. We should be wary."
What does that mean? You saw an ad, this ad seems perfect, the house, it seems to be superb, the right size, the right location, the right orientation, not too expensive, everything seems really perfect. And then you say: "Hmm... You have to be careful, all that glitters is not gold", it means you shouldn't trust appearances.
Maybe it looks perfect on paper in the listing, but maybe it's just a facade, maybe the house isn't what it seems. Just because it looks great in the listing doesn't mean it is great. So here, they say "all that glitters is not gold." Beware, this house looks great. Maybe it isn't.
In another context, someone might say, "I regret taking that promotion at work. I should have known. All that glitters is not gold." So this person got a promotion, they were offered a move up in their job, and they regret taking it, they say, "I should have known. All that glitters is not gold."