Invest: Independent, the story should not depend on other stories
iNvest: Negotiable, the story could be changed before and during the sprint
inVest: Valuable, it should deliver value to stackholders
invEst: Estimable, (self explanatory, right?)
inveSt: Small, a story should be enough small to be planned/prioritized
invesT: Testable, should contains "how to test" or "acceptance criterias".
