Spending more isn’t the problem, it’s the shrinking margins that kill you
The Google bid simulator is a funny tool, and sales and support staff can be interesting too. Neither account for which industries a term may or may not be relevant for, either the ones in the campaign, or the ones in the query space that appear with them. Nor do they consider the different value per sale competitors may have.
Freed from these constraints it is easy to assume that sales will increase with traffic as the bid per click goes up, and that all traffic is created equal, and all campaigns in an account operate under the same cost per acquisition targets.