A jar of candy sitting on your desk is going to tempt you over and over again. You may resist the first several times, but eventually you'll give in. Move the bowl further than arm's-reach away and bingo, your munching frequency goes down.
Wansink calls this temptation to eat without thinking "Mindless Eating" and he's even written a book about it with that very title.
How can we avoid falling prey to this weight-gaining behavior? Keep serving bowls off the dinner table and don't snack directly from the bag. In other words, make it more difficult to mindlessly keep shoving food in your mouth.