What The Heck ?

I get electronic deposit for one of my jobs. It's great , I wake up on an alternate Friday morning and there is fresh money in my account to pay my bills. I earned it, I know it's coming. It's just nice that it is there when I wake up and I don't have to go to retrieve the check or wait for the mail to arrive and then go to the bank. It's convenient. However, every once in a while , I don't keep a daily balance and I total every thing up when the checks go in. Well .. .. today I did that and basically I'm at a zero balance. I'm not overdrawn, it's just that everything that went out was equal to the amount that came in this week. I just don't understand how I did that . Nor do I have a master plan to get a leg up over the next week. I'm scratching my head and wondering "What the heck" ?