By default, Mac OS X’s Finder keeps system files – which generally start with a dot, like .bash_profile – out of your sight. But that makes editing one of these files extremely difficult if you, say, want to customize your Terminal prompt.
Execute the following in terminal (to undo the change set TRUE to FALSE):
defaults write com.apple.finder AppleShowAllFiles TRUE
You’ll need to option-click and hold on the Finder’s Dock icon, and then relaunch the Finder to see your changes take effect.