14. Even if you were destined to live three thousand years, or ten times that long, nevertheless remember that no one loses any life other than the one he lives, or lives any life other than the one he loses. It follows that the longest and the shortest lives are brought to the same state. The present moment is equal for all; so what is passing is equal also; the loss therefore turns out to be the merest fragment of time. No one can lose either the past or the future - how could anyone be deprived of what he does not possess? So always remember these two things. First, that all things have been of the same kind from everlasting, coming round and round again, and it makes no difference whether one will see the same things for a hundred years, or two hundred years, or for an infinity of time. Second, that both the longest-lived and the earliest to die suffer the same loss. It is only the present moment of which either stands to be deprived: and if indeed this is all he has, he cannot lose what he does not have.
15. 'All is as thinking makes it so.' The retort made to Monimus the Cynic is clear enough: but clear too is the value of his saying, if one takes the kernel of it, as far as it is true.
The eternal now. Book 2, passage 14 is a key concept to grasp. So many people fret and worry about what has been done (in the past). But they cannot correct it - they cannot go back and change the past. Equally, there are so many people who fret and worry about the future. Again, they cannot change the future and they have no control over it. Try as hard as you can, there will always be things you cannot control in the future. No amount of planning will prevent some things from happening.
What are you left with since you cannot change the past and you have no control over the future? You have now - this exact moment in time.
When I teach this concept to people, I like to draw a line on a whiteboard or chalkboard, saying that it represents time. An infinity in the past and an infinity in the future. And on that line is a speck in time representing now. When some religious people get hung up on anxiety about their past or their future, this drawing shows them that they are on the same line now as they have been in the past and as they will be in the future. So, in a sense, they are living eternity now.
Now is all the time you have - nothing more, nothing less.
Passage 15 of book 2 is the discipline of assent in a nutshell - we can make whatever opinion we want of events.