The outlet's potential is 230 V, the earth's potential is 0 V. The person touching the outlet will get shocked, but why? What is the path that completes this circuit so current will flow?
The neutral side of the 230 V line is connected to earth ground. Just touching the 230 V hot wire by itself won't hurt you, but if you are also touching ground or anything that is grounded, then there is a closed path from the 230 V thru you to ground thru the transformer and back to the 230 hot wire.
Not touching ground is a lot harder than you may think, since there are various things around you that you take for granted but could be connected to ground. For example, the chassis of your computer, the kitched faucet, the concrete floor in the basement, and even the screw holding the plastic plate over the outlet. Since many people aren't going to understand all the limitations, and it's easy to screw up and touch ground even when you do, it's better to just say that the 230 V line is not safe to touch. Most of the time under most conditions it's not, and the consequences of getting it wrong can be serious.