Many games available in the market requires multiple playthrough inorder to get all endings. However in Deus Ex: Human Revolution gamers can get all four endings in one playthrough only.
If you are among one of those aiming for 100 percent trophy or achievement completion, viewing all four endings is one of the requirement. There's no need for everyone to play the game four times to get all four endings, there's a way to get it.
How to View all four endings of Deus Ex: Human Revolution at once:
When you reach the Broadcast Center in Panchaea (final room in the game), you will get have a choice that determines what ending you will get. Keep in mind picking either one will giv you the one ending. Save the game and reload to view the other.
The other two ending in the game depends on the choice you pick when you have a conversation with David Sarif or Bill Taggart in Panchea. You will be given a choice as well and by using the same SAVING and RELOADING method, you can get all four endings in total.
To have a conversation with David, he can be found on the room where other survivors are barricaded in the Machine Room. Taggar is located in the locked Server Room. The option you will have to pick will depend on whoever person you would like to broadcast their message.
To cross check that you viewed each ending, let the credits roll or at least skip it then you can reload.