A beautiful story from shortly after the Buddha's parinibbana, as told by Luang Por Chah:

"The day before the first Sanghayana [Sangha Council], one of the Buddha's disciples went to tell Ananda: 'Tomorrow is the Sangha council, only arahants may attend.' Ananda was at this time still unenlightened. So he determined: 'Tonight I will do it.' He practiced strenuously all night, seeking to become enlightened. But he just made himself tired. So he decided to let go, to rest a bit as he wasn't getting anywhere for all his efforts. Having let go, as soon as he lay down and his head hit the pillow, he became enlightened."