Learn from mistake

I accidentally press enter when typing command mv {firstfile,secondfile} and my intend is to write smth like mv {firstfile,secondfile} destination/.

and as a result, the secondfile is overwritten by firstfile.

Prevent it from happening again

It's a good idea to always comment an important command: # some command that need executed cautiously and go back by C-a and delete the comment with C-d.

thanks for IRC folks that suggest to make it a habbit, will do it from now :)

see bash(1), specifically under section Commands for Moving to get more details on default bash keybinding.