http://revach.net/article.php?id=1784

Section:  Avodah   Category: Shmoneh Esrei
Part 21 Shmoneh Esrei: Modim - Unknown Miracles and Uncollected Debt

One should give Shevach to Hashem for his wonders because "ein baal hanes makir niso"; one who has a miracle performed for him does not recognize that there was a miracle. And every day there occurs for a Jewish man many miracles and he doesn't notice them, as it is written "L'oseh niflaos gedolos levado--Who makes great wonders alone," (Tehilim 72:18). The verse means that HaKadosh Baruch Hu alone recognizes the wonders and miracles and a man does not. If it were not for the miracles, we would, chas v'shalom, have been destroyed because all the Sarei Maala (chief angels of the nations) and the mazelos of the heavens wage war against us as it says "rabim lochamim li marom..."; many fight against me above.

He should especially give thanks on the return of his soul (every morning) as explained in the Zohar "a man who has a deposit from another and the other owes him money, would he not collect his loan from the deposit (in his hands)? And we deposit our souls every night in the hands of Hashem and he returns it every day and does not withhold it for what we owe Him great debts in our many sins. Therefore the Zohar says that there is to learn from Hashem to not grab the deposit of another even if he owes you a debt. He who grabs does not have "hemnusa kadisha"; holy faith. Therefore it is incumbent on us to thank and give praise to Hashem.

This is a short, practical version of Ya'aros Devash 1:1 which Rabbi Shlomo Wolbe zt"l condensed in Alei Shur pg.123. The original contains all kinds of fascinating mystical insights. The interested reader is referred to Ya'aros Devash 1:1, starting about half-way through.