Chazal (the Sages) tell us: Literally, it means that the person to whom Hashem does a miracle doesn't even realize it. The Ya'arot Devash writes that every day we have numerous miracles done for us, and we don't even realize it. He says that's why we thank Hashem in Modim three times a day and add the words, “for the miracles that you do for us every single day.” We say in the Tefillah (prayer), “If Hashem wasn't protecting us, the Goyim (non-Jews) would have swallowed us up alive.” The Kav HaYashar writes: “Because of all the thank you korbanot (offerings), we owe Hashem for the countless miracles He performs for us.” But I once heard another explanation of Ein ba'al hanes makir b'niso. Even when we do realize that a miracle has been done for us, we don't truly understand how beneficial it really was. We aren't capable of fathoming the extent of Hashem's chasadim (loving-kindness). The Pasuk (verse) says, and the Sfat Emet explains, “Thank Hashem for His goodness.” When you're thanking Hashem, have in mind that His chesed is endless. We are mortal and short-sighted, but Hashem is eternal and big, and His chasadim are boundless.
Rabbi Falk once gave an example. He said, “Imagine someone has a child. What a beracha (blessing). But what's our immediate joy? There's a baby in the house. It's so cute. We can play with it. But do we realize the extent of this chesed Hashem, both in this world and the next? The child will, be'ezrat Hashem (with Hashem's help), do millions of mitzvot (commandments) in his lifetime. And the parents who gave him chinuch (education) will be rewarded for everything the child will do. This child will teach his son properly, and that was only because of your education. So you get the rewards of the next generation as well. Who thinks of this when they have a baby? The child will, be'ezrat Hashem, have many children of his own, some of whom might be very important for Klal Yisrael at large. And it's all credited back to you. We are grateful for a healthy eight-pound baby, and that itself is a huge reward. But what really lies in this gift is beyond our hasagot (understanding).”
When Rachel Imeinu finally had her first child after all those years, she named him Yosef, because, as the Pasuk says, Hashem had taken away her disgrace. Rashi quotes the Midrash (rabbinic teaching) that one aspect of her disgrace was that a childless woman is blamed for anything that goes wrong or breaks in the house. But when there's a baby, the blame is placed on him. And everyone asks, “That's what she's thanking Hashem for?” Rav Gedalia Schorr explained: “Of course Rachel knew that this child was going to give her a share in the destiny of Klal Yisrael. But she wanted to tell Hashem that she realized how far this chesed really extended. It will even take the blame off me when something breaks. A very trivial matter.” We say in the Tefillah, “We will never fully be able to thank you, Hashem.” But it's a great level just to realize the truth of that statement. Shabbat Shalom.