Well agile techniques recommend you don't fix scope, and budget at the same time. Allowing you to go back fix your code that has turned out to be wrong. You're

Well agile techniques recommend you don't fix scope, and budget at the same time. Allowing you to go back fix your code that has turned out to be wrong. You're allowed to learn and to adjust your plan as you go a long. Waterfall people have to meet a deadline and a defined scope, so when being told that you have to refactor some code, the response is to ignore it to meet the deadline. In order to meet deadlines and a defined scope the plan MUST NOT change, otherwise the deadline or scope has to be changed as well. That is until you reach the deadline and find it doesn't work the way the customer wanted anyway because you refused to change the plan. For agile techniques the measure of progress is working software, not meeting set deadline and scope.