Never get influenced by…XYZ

Most of us might of experienced this type of situation like…missing very simple scenario during testing. Recently I had experienced this type of situation.
Expectations set to Test team for that particular drop is look for
-> No Application crashes.
-> Performance should be improved when comparing to the previous drop.
We tried all possible scenarios including positive and negative also .We found couple of observations, as most of them were classified as least preferred scenarios, those issues were deferred to next release and that particular drop was released to Production. We thought all the basic functionality would work as there is no specific code change but in production it happened in other way, the basic scenario was failed. When that issue reported to me I really did not believe myself how I missed out this...but fact was I missed it. Hope you all can guess the rest of the story L.

Lesions Learnt:
Never ever do sign off on the build without executing below mentioned test cases, especially when the drop is scheduled to deploy into Production.

-> Priority 0 Test Cases.
-> Frequently used scenarios.
-> Critical Scenarios.

Above test case results may give some sort of assurance that the particular drop is decent enough to deploy into production.
Any inputs???