Fall through the cracks

[Chucha]

I guess this is kinda new idiom, but have no idea what it means. The context is broad, as I presume :)

Thanks to all for their ideas.

[Тruth Seeker]

To pass unnoticed, neglected, or unchecked: “In the past, many learning disabled children fell through the cracks” (Judith Harkness Richardson).
http://dictionary.reference.com/search?q=fall+through+the+cracks&r=66

[Дакота]

http://multitran.ru/c/m.exe?SearchAnswers=ON&a=fsearch&L1=1&L2=2&ft=2&q=through+the+cracks

[Дакота]

обычно говорится о людях, оказавшихся в неблагоприятном положении из-за несовершенства системы/законодательства