The proverbial mormon shelf is a place mormons are encouraged to place all their questions (especially the unanswerable questions). They are asked to have faith that the questions will be answered later, and sometimes not even in this lifetime. Either with greater spirituality or more knowledge via revelation we’ll be inspired to know the answers to key issues that can’t currently be answered in a “faith-promoting” manner. Individuals end up with a heavy shelf over the years until during some faith crisis, the shelf breaks. In this process, many realize that they knew the answers to these questions all along if they were honest and brave enough to really think about it. The answer is not faith-promoting though, so there’s no way to continue the current belief.
This site allows mormons who leave the church to create a profile and list their shelf items as well as contribute answers to some of these questions. Here is the growing list of shelf items, click them to view those who contributed their stories with the associated term on their shelf.