Watch What You Wish For

There is a frightening Metzudas Dovid in today's haftorah for parshas Korach. In Shmuel I, chapter 12, pasuk16, Shmuel rebukes the Jewish people for asking for a king.

Metzudas Dovid says, Shmuel says, "If you will say, if asking for a king was considered bad by Hashem, why did He agree" and give us a king, Shaul?
"To this I respond, even now, after He agreed, stand by and see this great thing [and Shmuel says, it's the wheat harvest now (not a time when it rains) and I will call to Hashem and He will give thunder and rain ...] and from this you will be able to understand the ways of Hashem.  Hashem fulfills the request of a petitioner even if it is bad in the eyes of Hashem, and even if to the petitioner it will not be considered beneficial."

Apparently, this is why we use the phrase: may all mishalos libeich l'tova be fulfilled - all requests of your heart for good, leaving it up to Hashem to determine what is good for us.