If a soldering iron melts solder, why does solder stick to the tip when you tin it?

Question

If a soldering iron melts solder, why does solder stick to the tip when you tin it?

Answer 1

Surface tension

Answer 2

Did you expect it to run off?  It is still on the tip, even in molten form, providing a de-oxidised clean surface.

Answer 3

The liquid lead-tin mixture "wets" the tip of the soldering iron much like water wets objects with which it comes in contact.  Get enough solder on the tip and it will run off just like water would.  We can also see the wetting action of the liquid lead-tin mixture because of the action of a "solder wick" which is used in desoldering a connection.  Only a "wetting" substance can be wicked.