There are five modulations of the mind:
First, the mind wants proof for everything. How can you get proof for everything? Impossible!
First, the mind wants proof for everything. How can you get proof for everything? Impossible!
Second, the mind does not understand things the way they actually are, but thinks something else. You thought something; a little later found out it was not actually like that; a little later, concepts break down. This is called Viparyaya.
Third, the mind has its own imagination; when nothing of the sort actually exists.
Fourth, the mind falls asleep. If it is not thinking of anything, then it falls asleep.
Fifth, the mind is stuck in the memory of the past, or worried about the future.
These five modulations prevent one from being alive in the present moment and enjoying it.
Yoga brings the shift; it helps you to sail over the modulations of the mind.

Sri Sri Ravi Shankar