Albert Einstein said:
The only thing that interferes with my learning is my education.
Staying in the office or lab, and researching and trying to figure out the best approach for the best product – is a waste of time. Instead you need to bring your ideas to the real world, get feedback, iterate and continue develop.
To “get out of the building” means exactly that; Having a brief brainstorming in the office, quickly developing a basic prototype, and bringing it to the public, the target audience in short time. The sooner you get out of the building, the better. You then have valuable feedback, to continue iterating your product development and process building.
By staying “in the office” you have your thoughts only, which are not new, and are not the market’s opinion and thoughts of your solution and product.
Steve Blank mentioned this concept of “getting out of the building”, early on and many times since. Getting out of the building helps you understand and build the Minimal Viable Product (MVP).