Why do I get 800A01C2 errors?

I think we've all seen this one: 
 

Microsoft VBScript runtime error '800a01c2'  Wrong number of arguments or invalid property assignment: '<object.method>'

 
This can happen when trying to call a method like a property, or vice-versa; or by calling a method of a built-in object, and passing in too many arguments. 
 
However, the most common cause I've seen for this is using ADODB.Recordset to create a new record, and then have something like this: 
 

<%      ' ...      RS.Fields.Item("ColumnName") = "someString"      ' ...  %>

 
To resolve, you have one of two options. The first is to use an INSERT statement directly against a connection object; this is both more efficient and less error-prone. The second is to use either of the following syntax styles: 
 

<%      ' ...      RS.Fields("ColumnName") = "someString"        ' or        RS.Fields.Item("ColumnName").Value = "someString"      ' ...  %>