There have been a lot of instances when you have been accidentally deleted important file which was unrecoverable. Your data can also lose due to corrupted hard disk. But there are ways to recover your data no matter how grim the situation is. Disk Drill is a data recovery software for Mac OSX that can recover data from HFS/HFS+, FAT, NTFS and other file systems right from your Mac.
Disk Drill (currently beta, so it is free) will locate and recovers deleted files photos, music, documents, applications, etc) from any mountable media like your main drive, external hard disk, memory cards, etc.