Can you achieve something without getting out of your comfort zone?

Yes. Because comfort zone is a personal thing. For some, it's playing video games. For some, it's cooking at home. If it makes you happy, you are achieving something. Getting out of your comfort zone means being uncomfortable and having a new experience.

Probably you can - but the satisfaction you'll get from it won't be very high

Of course you can :) but in most cases, getting out of your comfort zone will allow you to get better results and you will get the most of this experience!