I see mentorship as an excellent shortcut to self-improvement, as it is a good way to quickly get quality feedback. But finding people that you can model works as well. I've personally learned a lot just looking at how other peers approached problems. If you work in an environment where there is no true role model, you often end up becoming the role model yourself, as you decide on what is important or not. At this point, the internet is your community, and if you work with your office's door closed, you might dig yourself into a hole.