5 ideas
Nature gave us possession of only one thing: time. Yet people guard money and property jealously while letting others take their hours freely, and they never count that loss because time is invisible and cannot be repaid. The most shameful waste is the time lost through carelessness, because most of life slips by while we are doing nothing or doing the wrong thing.
Set aside a few days at regular intervals to live on the scantiest, cheapest food and in coarse, rough clothing. Then ask yourself, 'Is this what I used to fear?' Having actually lived through the feared condition while secure, the mind loses its dread of losing wealth, and it is trained for hardship before hardship arrives.
Visiting his suburban villa, Seneca scolded his steward for the crumbling building and the gnarled, leafless plane trees, then realized he had planted those trees himself and the building had aged alongside him. He asked who the decrepit old man at the door was and learned it was Felicio, son of his former steward and his own childhood playmate. From the moment he saw his own aging reflected in things around him, he argued that old age should be embraced and each day lived as a complete life.
Seneca went to the midday arena show expecting wit and relaxation and instead found pure slaughter, with the crowd demanding more killing. He came home greedier, more cruel, and less humane, simply from having been among people. The mechanism is exposure: any one person who displays a vice passes it on without trying to, so a mind still in training should withdraw from crowds and keep company with people who will improve it.
Before admitting someone as a friend, deliberate carefully about whether they deserve it. Once they are admitted, trust them as fully as you trust yourself, sharing every concern and plan. Treating a friend with suspicion teaches them to deceive, while deliberating after committing reverses the proper order and ruins the friendship.