Gemara: From that which it says, "For the squeezing of the milk produces butter, and the squeezing of the nose (af) produces blood, and the squeezing of anger (apayim) produces quarreling" (Mishlei 30:33), we derive the following. Where do you find the "butter of Torah"? With one who spits up the milk that he nursed from his mother by studying Torah. From the metaphor of the nose (af can mean nose or anger) we learn that a student whose teacher got angry at him once and he was silent will merit distinguishing between blood that is pure and blood that is impure. From the metaphor of anger we learn that a student whose teacher was angry at him twice (apayim can mean double af) and he was silent will merit to distinguish between monetary law and the laws of capital punishment, as R. Yishmael said: One who wants to be smart should study monetary law, as there is no subject that surpasses it, for it is like a flowing wellspring.

Ein Ayah: Many Torah educators strive to find ways to lighten the yoke of studies. They believe that by enabling students to acquire much Torah knowledge in a simple manner without great toil brings blessing. However, the gain from this approach is dubious, as knowledge should be valued based on quality, i.e., deep understanding and sharp application of the knowledge in many areas. This is especially true of Torah knowledge, which is to make a significant impression on the learner in regard to ethics, good deeds, and fear of Hashem.
To reach these goals, one needs knowledge acquired not through techniques for easy digestion of material, but on hard intellectual work. Such effort elevates him to good attributes, a love of intellectuality and holiness, and full dedication to the study. In contrast, that which is acquired without toil will remain external to a person’s soul and stagnant and will have little impact on his actions and his moral state
That is what the gemara means by the butter of Torah, i.e., its best part – the highest intellectually, which evokes the most righteousness. This is acquired by he who began by separating himself from childhood with its regular longings, so that his Torah not be that of childishness. This is what the gemara means by spitting up the milk he nursed, as the hard work makes him reject the "nourishment" that he received with excessive ease, as a growing child rejects his mother’s milk, which is readily digested and available. Specifically the hard work is what should excite the youngster and cause him to want to spit up that which he learned too easily, which is tainted by superficiality.
Practical knowledge is built around a variety of areas of knowledge, and one is first required to be familiarized with the area. Experience teaches one to make fine distinctions, like that between different types of blood. One who is willing to suffer through the experience of subservience to his teachers will reach the next level of intellectual attainment – understanding matters in an all-encompassing, not a detailed oriented, manner.
The following is the difference between monetary matters and capital offenses. Matters of justice consist of elements that are specific to the case and those that are connected to external matters. Monetary justice is, to a great extent, created to remedy injustices between man and man, which links it to the needs of society in the present and the future. Capital matters usually stand on their own, and therefore basic unchanging rules of justice are employed. Due to this distinction, monetary justice is more dynamic than capital law. In general, monetary matters are the most complex halachot, requiring one to master general factors and apply them to very specific situations. Only one who suffered at the hand of his master twice, corresponding to the realm of relationship with him as a general mentor, and as the teacher of a specific course of study, is assured success.