2. Difficulties are people's textbooks.

3. Everything is difficult at the beginning, so is every science. -Marx

4. Grey theory is everywhere. My friend, only the green trees of life are evergreen and lush. -Goethe

5. The virtue of prosperity is temperance, and the virtue of adversity is tenacity. The latter is a great virtue. -Bacon

6. Being proud is not necessarily the driving force of life, and being frustrated is not necessarily the fetter of life. Those who dare to face life directly and be content with indifferent life are the people with the freest soul and the most complete personality.

7. The greater the difficulty, the greater the glory. -Cicero

8. Difficulties are teachers who are extremely solemn. -Burke