Not all defects cause a failure. For example, a defect in [[dead code]] will not be considered a failure.
A defect that does not cause failure at one point in time may laterlead occurto failure later due to environmental changes. Examples of environment change include running on new [[computer hardware]], changes in [[source data|data]], and interacting with different software.<ref>{{Cite web |date=March 31, 2011 |title=Certified Tester Foundation Level Syllabus |url=https://www.istqb.org/downloads/send/2-foundation-level-documents/3-foundation-level-syllabus-2011.html |access-date=December 15, 2017 |publisher=[[International Software Testing Qualifications Board]] |at=Section 1.1.2 |format=pdf |archive-date=October 28, 2017 |archive-url=https://web.archive.org/web/20171028051659/http://www.istqb.org/downloads/send/2-foundation-level-documents/3-foundation-level-syllabus-2011.html |url-status=dead }}</ref>
A single defect may result in multiple failure symptoms.
