Well, problem number one is that you're trying to do volume of butter instead of weight. All the sticks are by weight, so even though they're marked with tbsp on the side (8), the stick is a quarter lb (4oz). So the notional volume is 4 fl oz, and the weight is 4 oz, but the density is not equal to water.
The other problem is that density of things can vary wildly. Flour can be 30% different in density depending on how you scoop it ( scoop it into the measuring cup vs scooping with the measuring cup).
And of course problem number three is not converting your measurements before you start cooking, just like it's a problem not to mise-en-place your ingredients first. (If you mise-en-place, you've probably got the correct measures of ingredients already).
The other problem is that density of things can vary wildly. Flour can be 30% different in density depending on how you scoop it ( scoop it into the measuring cup vs scooping with the measuring cup).
And of course problem number three is not converting your measurements before you start cooking, just like it's a problem not to mise-en-place your ingredients first. (If you mise-en-place, you've probably got the correct measures of ingredients already).