Quite the opposite is true of assistant directors on films/television. There is a highly structured assistant director universe and the rules are manifold. The three tiers of assistant director have completely different jobs. The 1st AD helps to prepare the script breakdown and the schedule and is always on set once principle photography has started. Sometimes with a megaphone. They control much of the ebb and flow of set life and call out the 'Standby' and 'Turnover' instructions and sometimes even 'Action' if the director is too shy or forgetful to do so. They know pretty much everything that is happening on and around the set at any one time and they entirely rule the lives of the 3rd ADs. Some directors like to work with maniacal 1sts and some prefer the quiet but firm types. They are usually men. The 1st AD does not work with the actors and is not usually interested in being a director; they will be more likely to go into the production side of filming. If the 1st AD is a bastard, life on set is miserable.
2nd ADs are hardly ever on set. They stay at the unit base (often a collection of motley caravans in a car park) and work in their office. Occasionally they emerge and hand out the call sheets they have spent all day changing as the schedule finds new and inventive ways of collapsing. They liaise with the costume, make-up, facilities and catering personnel at the base and try to get the actors on to set when they are supposed to be there. Sometimes they have a bus full of extras to keep warm and feed. When things are going wrong at the base, everyone complains to the 2nd AD. They have thick skins.
The 3rd AD is told what to do by everyone, except the extras, who they direct. They are often on set, unless someone has forgotten something back at base. They have walkie-talkies with earpieces so that no one else can hear the obscenities and indiscretions being yelled at them by the 1st AD. In the middle of a conversation about just how drunk they were the night before, they will suddenly press their hand to their ear, go white, then red, then run somewhere. They must keep the actors in their line of vision at all times, even when they go to the bathroom. Actors wander off.
The runners answer to the 1st, 2nd and 3rd ADs. They work the same hours, they are paid less. They have to really want the job.
As an actor, you spend time on set with the 1st and time at the base with the 2nd but your every moment on standby is passed in the company of a 3rd or a runner. This can be many, many hours. They will get water, tea and coffee for you. They will relay messages, make sure you are comfortable, even laugh at your jokes. This is not because they like you; they just don't want you to leave the standby location. If you leave, they will have to follow you. They will also have to explain to the 1st why you have left and where you went, if you are called. Sometimes actors get upset they are being followed everywhere, then the 3rd will still follow them but they will hide. If you turn around quickly you will see a 3rd ducking into an doorway some 50 meters behind you. When the actor goes on set, the 3rd will announce their imminent arrival on the walkie-talkie. 'On their way!' Goes the cry. '1 minute!', '30 seconds!', 'Stepping on!' and there you are, how nice.
Finishing a film is a series of small adjustments but one of them is getting used to being unannounced when you enter the kitchen.