Is it ever ok to not test a feature?

Is there any point at which you become so familiar with your language/database/system that **there is no need** to test a new feature/configuration/query/etc. by contained/simulated testing before implementing it in your system (especially concerning a feature that modifies data)? Or is it *always* essential to test a new query *by simulation in a test environment*? To specify further, it is clear that it is always **safest** to test. However, is there a way to determine when the risk is so minimal that testing is not worth the effort? Another way of phrasing that: when or is it ever **professional** practice to take a measured risk to implement a feature? Also, let's assume that everything is backed-up, so, worst-case scenario, the data *could* with some effort be restored. Can someone cite specific, expert experience to address this? Please include references where appropriate/possible.