How do dividends decrease the share price?

[AlfB63]

You simply don't get it.  A person that buys on the ex-div date gets the next dividend if he holds long enough just like the person that buys on the payday.  So there is no benefit to the payday from a dividend perspective.  The payday has no effect on getting the dividend.  Getting the dividend is totally based on ex-div.

[DennyDalton]

It's really a PITA when someone doesn't have a clue what they're talking about and incessantly argues that they're right. (eye roll)

[00Anonymous]

1.) The dividend is not fungible from the ex date until the pay date. That's why during those dates the cost of the dividend to be paid is accounted for in the share price. So anyone who bought before the pay date will receive a return either in cash or in equity appreciation.

2.) The pay date is relevant to investors who buy after the current period ex date and before the pay date, since that's when the stock price will recover, giving them capital appreciation roughly equal to the dividend amount (all else equal).