The philosophy
To begin, we must consider the philosophy of the ZBS to be very unorthodox compared to the what the game was originally designed to be. The core of this scheme relies on teamwork and ganging up on defenders rather than specific assignments. It is the reason why it is difficult to draw up a ZBS play, because offensive lineman probably won't know who they will block until they are set at the line of scrimmage. However, this allows the team to predicate how to open up running lanes based on specific looks by the defense; so, whether there are eight guys in the box or six, the trenches are always prepared to do their job.
Another reason the ZBS is successful is due to its balanced nature. Standard offensive lineman are typically asked to either run block and drive the line of scrimmage forward on a play, or pass block and move backwards to form a pocket.
In the ZBS, there is no such distinction, because the most important direction in ZBS for a offensive lineman is laterally in either direction. Having the offensive line either move right and left instead of back and forth forces the defenses to be more attentive in recognizing whether or not the offense is passing or rushing.
ZBS requires a specific type of offensive lineman to work. You can't just be big, you can't just be tall, and you can't just be fat either. Can your center immediately recognize what front the defense is in? How good is your right guard in terms of cut blocking? Does your left tackle have enough athleticism to swing around and get the correct angle on the defensive lineman? All these questions are ones that a coach needs to ask before even trying to implement the scheme. If there aren't any concerns, then it is time to move on teaching them to proper skills.
