Why does the market fall ahead of F&O expiry or expiry day?

I have observed that the market falls ahead of expiry or expiry day. Can someone explain to me in layman terms why that is so ?

Doesn’t happen all the time. If you think it does, don’t you think the easiest way to make money is to short as much as you can since you’re assured that it’d fall?

coz of index management n moreover open position are sq off .

In few words, Max. Option Pain.

The Index moves to an area where there is max. pain for option buyers / least pain for option sellers.

The only exception is when it is FIIs who are the Option Buyers.

It might be part of the manipulation.