Yes it is possible to earn Bitcoins even without investing fiat or funds coming out from your pocket like joining signature campaigns in this forum (if you are qualified) you will be paid in Bitcoins. For me, I started with faucets (lots of them) and joined some contests in games and rounds section and when I finally reached a status that I can join campaigns, I joined and earned Bitcoins. You can also do some tasks and get paid in BTC.

There's a lot of ways to earn Bitcoin, you just have to step out of the box and don't focus on just one way to earn.