Weights and shackles Seneca offered the following advice:

[Reflect] that prisoners at first find the weights and shackles on their legs hard to bear, but subsequently, once they have determined to endure them rather than chafe against them, necessity teaches them to bear them bravely, habit to bear them easily. In whatever life you choose you will find there are delights and relaxations and pleasures, if you are willing to regard your evils as light rather than to make them objects of hatred. In no respect has Nature done us a greater service, who, as she knew into what tribulations we were born, devised habit as a means of alleviating disasters, swiftly making us grow accustomed to the worst sufferings.

This passage suggests Seneca was well aware of at least one phenom enon discussed in Section 9.5. Which one?