sql: improve kill's description (pingcap#6233)

sql-statements/sql-statement-kill.md

@@ -33,8 +33,9 @@ Query OK, 0 rows affected (0.00 sec)
 
 ## MySQL compatibility
 
-* By design, this statement is not compatible with MySQL by default. This helps prevent against a case of a connection being terminated on the wrong TiDB server, because it is common to place multiple TiDB servers behind a load balancer.
-* The `KILL TIDB` statement is a TiDB extension. If you are certain that the session you are attempting to kill is on the same TiDB server, set [`compatible-kill-query = true`](/tidb-configuration-file.md#compatible-kill-query) in your configuration file.
+* By design, `KILL` is not compatible with MySQL by default. This helps prevent against a case of a connection being terminated on the wrong TiDB server, because it is common to place multiple TiDB servers behind a load balancer.
+* DO NOT set [`compatible-kill-query = true`](/tidb-configuration-file.md#compatible-kill-query) in your configuration file UNLESS you are certain that clients will be always connected to the same TiDB node. This is because pressing <kbd>ctrl</kbd>+<kbd>c</kbd> in the default MySQL client opens a new connection in which `KILL` is executed. If there are proxies in between, the new connection might be routed to a different TiDB node, which possibly kills a different session.
+* The `KILL TIDB` statement is a TiDB extension, which is a different syntax from the MySQL `KILL [CONNECTION|QUERY]` command and the MySQL command-line <kbd>ctrl</kbd>+<kbd>c</kbd> feature. It is safe to use `KILL TIDB` on the same TiDB node.
 
 ## See also