i am creating a game similar to this.

[matches81]

First off, don't steal game concepts. Second off, if you need to ask that you should not be making a game. Third, you should write your own engine.

I'm an indie game designer, and those are the staples of success!

You may be an indie game designer, but I still think those are some pretty odd statements.
a) The OP isn't talking about stealing a whole game concept. He's talking about implementing the ability to throw items and that he wants to make a game similar to Penumbra. To be frank, most games are similar to some other games out there and if you insist that the game you're going to make has to be different from anything the world has ever seen you're probably not going to make any game at all.
b) People have to ask questions to learn things. Perhaps he should not be making a game already, or perhaps he should find programmers to help him because he's better at designing stuff than at actually implementing it, but to be honest: We don't know that. Telling him he should not be making games just because he asked a simple question is overly harsh and, IMO, entirely uncalled for, seeing we know absolutely nothing about the guy.
c) There are tons of great games out there using a third party engine instead of their own. Writing your own engine is not a staples of success, it's a risk. More often than not, people intending to write their own engine prior to making a game don't ever get to the point of making the actual game because writing the engine takes up their whole time and drains them of any enthusiasm. Luckily, for people like that, there are tons of third party engines, many of them free to use. Why discourage that?