A finish is two things: resin and oil. Most people only know about one of them.
You know that white ring on your dining table.
The one that appeared after a glass of water sat there for twenty minutes.
You tried everything. Mayonnaise. A hairdryer. That wood pen from the hardware store. It faded a little. Then it came back.
Here is why.
The finish on your furniture is made of two things: resin and oil.
Resin is the hard shell you can see and touch. Oil is what keeps the resin flexible.
When the piece was new, both were present. The resin was firm. The oil was alive. Together they could absorb a water ring, take a scratch, and spring back.
The water ring is not moisture damaging your table.
It is moisture walking through cracks in a shell that stopped protecting the wood years ago.
The oil left. Slowly. Without you noticing. And the resin has been brittle ever since.
PROOF
Watch: water ring disappearing on application ▶