I think you meant "diminishing marginal utility". The law of diminishing marginal returns concerns employees not goods consumed.

Though not specifically relevant to your post, this "law" doesn't always hold. Some goods have a utility threshold that must be crossed before they become valuable or increase in utility (e.g., various medicines and antibiotics). Money operates similarly, i.e., its utility does not necessarily diminish, much less in monotonic fashion. Assume that if I make N dollars, I may be able to afford popcorn or I may be able to afford butter, but not both. Let's also assume that I derive little satisfaction from popcorn or butter alone. However, if I make N+1 dollars, I can afford both popcorn and butter from which I derive a great deal of satisfaction. The addition $1 has greater utility than the Nth dollar I had previously.