This feels a little light

When someone gives you a bag of groceries and it feels like there's a few things missing because the bag feels a little light. So you go back to get the rest of the groceries. When someone hands you speed (Amphetamine, Ethylamphetamine) after you paid money and the gram of speed feels a little light more like two thirds of a gram to three quarters of a gram. So you weigh it and demand the rest, and they give you more. Or if you're buying 5 dollars of cheddar cheese and it feels more like 3 or 4 dollars of cheddar cheese so you ask for more. When you're in college studying organic chemistry, mathematics, history, geology, and you forgot a book because the bookbag feels a little light. When you make money selling coffee and the stack of money they pay you feels a little light today. When you ask a friend for half the energy drink and they only give you a third and you say this feels a little light, so they pour more. It means it's not enough or something is missing.