Three reasons why people might accidentally overdraw are:

Before answering the question, we need to know what overdraw means. So overdraw is basically the drawing the excess of money which the account of a person actually holds. In simple words, when the money in someone account is more than the amount he thinks. He thinks he has more amount in his account and when he tries to withdraw, he comes to know the real amount. This could be because of many reasons, three of which are as follows:

They withdraw the amount from ATM and they may not record it. secondly they may have made a mistake in their arithmetic while estimating their equity, and thirdly, they might have forgotten to make a deposit.

All these reasons could be the reason for overdraw.