The earlier you find a bug, the cheaper it is to fix it.
If you are able to find the bug in the requirements determination, it is going to be 50 times cheaper
(!!) than when you find the same bug in testing.
It will even be 100 times cheaper (!!) than when you find the bug after going live.
Easy to understand: if you find the bug in the requirements definitions, all you have to do is change the text of the requirements. If you find the same bug in final testing, analysis and code build already took place. Much more effort is done to build something that nobody wanted.
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