[@The book of bad juju] It's not necessarily an instant failure, it's just really hard to walk up to a guard and convince him that he should ignore the orders given to him by a considerably scarier man than you. But if you think you can get your hands on the materials required, feel free to give it a shot. It may take a lot more work to do it in such a way though, and by the time you finish researching your target and organizing your disguise, another operative could have been sent in and had the job done already.