The Yidden in the desert complained (Shemos 16:3), הבשר סיר על בשבתנו מצרים בארץ ... יתן מי לשובע לחם באכלנו, "If only...we were in Mitzrayim, where we sat near the pot of meat, and we ate bread to satiation." According to the simple meaning, they complained that they didn't have meat any longer and that they didn't have bread.
The Ketzos (Shev Shmatsa, hakdamah 6) quotes the Mahara'm Almushneinu, who explains that the most outstanding geniuses are those who have a drop of foolishness in their thinking process. They work to circumvent the foolish part of their mind, which makes them very wise.
The Mahara'm Almushneinu writes that a similar thing can be seen when a drop of water drips into a large bonfire. The fire becomes more vigorous. The water doesn't weaken the fire because the fire fights to overcome the water that tried to extinguish it. Similarly, we see that people who have straightforward minds are often not the smartest. But those who have a problem with their thinking process are forced to overcome that obstacle, which makes them even wiser.
This is alluded to in the pasuk (Koheles 10:1), מעט סכלות ומכבוד מחכמה יקר, "A person who is respected because of his wisdom and honor, it is due to a bit of foolishness."
The Mahara'm Almushneinu explains that the Torah calls the yetzer hara מאד טוב because it makes the person מאד טוב, very good. The yetzer hara places obstacles in a person's way, and when one overcomes them, he becomes מאד טוב.
The Alter of Navorduk zt'l taught the following parable:
A worm was inside the neck of an oil lamp, and it didn't know where to go. When the worm went up, it felt the heat from the flame that was lit above the lamp, and it backed down. But as it went down, it met with the oil, which is also not an option. Eventually, the worm fell into the oil and drowned.
This parable reminds us that we shouldn't back off when there are struggles. We should face them because through them we reach the highest levels.
As the Vilna Gaon said, יצליח העקשן, "Those who are stubborn [in the war against the yetzer hara] will succeed."
However, the Chasam Sofer zt'l explains that they couldn't have eaten the meat because it wasn't kosher. They were saying that they remember how it was in Mitzrayim, הבשר סיר על בשבתנו, when we sat next to the Egyptians who were cooking pots filled with non-kosher meat, לשובע לחם באכלנו, but we didn't partake in the non-Kosher foods. We passed the test, and we ate bread alone.
They were reminiscing about how it was in Mitzrayim when they were faced with great tests. They missed the tests because passing them is the purpose of life.
