A consumer might value and is willing to pay up to $5 for their first bag of chips. Yet they are sold for $2. For every additional bag of chips sold, the consumers willingness to pay diminishes. However, that might not be until after 20 bags. This is where the role of the budget comes in. If the consumer only has $20, they are only able to buy 10 bags - which is far below the level of which utility will be maximized. Therefore, income and budgets actually prevent consumers from maximizing their utility.