This is a great rule which helps overcome anxiety and leads to success in life in a general way. It helps preserve friendship and happiness among the family, because a high-minded person perceives well people's nature, considers all changes, puts himself in other people's place and assesses both the hidden and obvious situations.
When it comes to anxiety, a high-minded person understands well realities and knows, when faced with a problem or when he does not achieve what he wants, that this is the nature of life and that no one has it his way. Man may dislike something in which there is good for him, and may like something in which there is evil for him, but all the good is that which is decreed by Allah swt.
The person who has deep insight feels that he is part of this great universe, and accepts the fact that he has his share of pain grief and also happiness. Therefore, he is not mentally distressed or painfully affected by any affliction. He does not suffer from any feeling of persecution which is felt by the one with little insight, who feels that he is the only one stricken by such problem, or that people are victimising him, or that he always has bad luck.
A high-minded person does not feel such feelings. Rather, he understands well the nature of life, and that he is part of it; therefore, he is content with it, as he endeavours to achieve the best in his life.
"Enjoy happiness now and do not wait until tomorrow."
P.S I think there may several editions of this book, this piece is not from the one I usually use...