Don't punish yourself when you are too tired to meditate: 'I should be meditating; I am very bad.' You destroy yourself like this. Be wise. Treat yourself, your mind, sympathetically, with loving kindness. If you are gentle with yourself you will become gentle with others so don't push. Pushing doesn't work for me, that's why I tell others not to force themselves. We are dealing with the mind, not rocks and concrete; it is something organic.