You can field strip an M16 and an M1911 blindfolded.
You can plan and deploy Radio Direction Finding Net, you can keep it supplied with beans and bullets, and run the analysis and control element that will have the enemy headquarters pinpointed in an hour, along with reporting the commanders laundry list and what he had for breakfast. (Fish head soup and rice.)
You can trouble shoot a radio and get it on the air with a hand full of this-and-that that would have MacGuyver shaking his head.
But when the door guy is done, you have to call a technician out to determine that you re-installed the alarm system sensor backwards--actually, upside down--and fix it.