First of all: as the saying goes, things are rare. There must be fewer diamonds to preserve and increase their value (weight, color, clarity and cutting are all good or a few are good). In other words, a very ordinary diamond can be seen everywhere, and people don't need to buy it "second-hand". It is better to go directly to any jewelry company to buy a new one. Unless you are a celebrity, fans are rushing to take what you brought!
Secondly, the discount ability of diamonds is still relatively general, far less than that of gold. In other words, when you are short of money and have a piece of gold in your hand, you can immediately change it into RMB, but if you have a diamond, even a peerless diamond, it may not be accepted or turned into money immediately.
In the long run, diamonds still have investment value, especially the larger particles, but they should be treated correctly and rationally.