The old Lay's potato chip commercial says, "You can't eat just one." And, they are absolutely right.
This goes for most easily handled, processed, sugary foods. I watch my children handle treat foods like ravaged animals and try to put a stop to it by telling them sugar is poison or sugar eats your muscles. And, yes sometimes I'm right there with them.
But these sweet foods are so highly palatable. You can't just eat one. Cookies, chips, candy, overstimulate the reward/pleasure zones of our mind and it makes us so happy to continue chucking that crap down.
These little binges add a lot of extra energy or calories to our diet. Worthless calories that don't do anything but steal energy by giving us a quick boost of it. Don't be fooled by fruit juices, yogurts with sugar and fruit, fitness foods (like bars). They're packaged nicely but delivered with high sugar contents.
At the end of the day, if you could just eat one, you'd be okay. But, because of the enjoyment it brings to our palate and how our brains respond to them, we can't.
My advice, don't have them in the house. It sure is nice to pick up a bag of chips when you're starving, but if it's not available, you won't be tempted. Fill your house with fruits and high-quality snacks . Try a large glass of water before you dive into snacks, and make sure that you are eating at least three quality meals to avoid getting into "I'm starving!" mode.