IMSAFE is the fitness checklist remote pilots use under the §107.17 self-assessment. On both published FAA lists, S is Stress and F is Fatigue. The last letter is where the lists diverge. The Pilot's Handbook of Aeronautical Knowledge and AIM 8-1-1 spell the final E as Emotion. AC 107-2A Appendix A, paragraph A.4.8.2, spells it Eating. Emotion and Eating are different words. Know which source the question is using before you answer the E.
Two lists, one pair the question asks for
Section 107.17 says no person may manipulate the controls or act as remote pilot in command, visual observer, or direct participant if they know or have reason to know of a physical or mental condition that would interfere with safe operation. Part 107 does not require an FAA medical certificate. The checklist is how you do that self-check in a repeatable way.
The shared letters are Illness, Medication, Stress, Alcohol, and Fatigue. The question that asks for S and F keys Stress and Fatigue, and the explanation is explicit that those two match on both lists. Sleep and Focus are not the expansion. Stress and Fear are not the expansion. If the item only asks for S and F, you do not have to guess the final E to get it right.
The final E is the letter you must not collapse. AC 107-2A uses Illness, Medication, Stress, Alcohol, Fatigue, and Eating. The Pilot's Handbook and AIM 8-1-1 use Emotion for that last E. A question written from the advisory circular is asking about food and the physical effect of not eating. A question written from the handbook or AIM 8-1-1 is asking about emotion. Treating the two words as synonyms will pick the wrong source. Alcohol on the checklist connects to the separate limits in §107.27 and §91.17, covered on the Part 107 alcohol rules page. Medication that impairs faculties is a no-go under those same incorporated rules, even when the drug is sold over the counter.
Fatigue is fixed by rest
The fatigue item keys a performance fact. Fatigue degrades judgment and reaction time, and it is best remedied by rest, not by stimulants. Caffeine does not fully eliminate fatigue. Fatigue is not something that matters only at night. A short night before a noon job is still fatigue. So is a week of long days that leaves you slow on a sunny morning.
That pairs with §107.17. If you know you are fatigued enough that judgment and reaction time are off, you know of a condition that would interfere with safe operation. Pushing the flight because the site is only available today stacks fatigue on the external pressure described with hazardous attitudes. The systematic pause that should catch it is aeronautical decision-making, and the pilot slice of PAVE is exactly this checklist.
Off-center viewing for a dim object
The night-vision item in this set is about detection technique. In low light, the most effective technique for detecting a dim object is off-center viewing, using peripheral vision. Staring directly at the spot where you expect the object is the weaker technique. Looking at a bright light first is also the wrong preparation. The explanation keys off-center viewing because that is how you detect dim objects at night.
Off-center viewing means you look slightly to the side of where you expect the dim object, so peripheral vision does the detecting. A bright light in the eyes before you look is the wrong preparation, and staring straight at the expected spot is the weaker technique.
Seeing the aircraft still has to meet §107.31. Off-center viewing helps you find a dim light. It does not replace anti-collision lighting, and it does not replace the night-training condition in §107.29 when the flight is at night.
A hot afternoon and a dim twilight recovery
You slept four hours and drank coffee in the truck. The checklist's F is Fatigue, not Focus and not Fear. Coffee has not restored the judgment and reaction time the question says fatigue takes away. Rest would. You delay the flight. That is the remedy the item keys, and it is the §107.17 decision.
On a later day you are current for night and the aircraft has the required anti-collision light. At the end of civil twilight you are looking for a dim light against a dark field. You do not stare straight at the bearing where you think the aircraft is, and you do not flash a bright light into your eyes first. You use off-center viewing to pick up the dim object. The checklist's S, Stress, still applies: rushing the recovery because the client is waiting is a fitness problem, not only a stick-and-rudder problem.
If a question stem quotes AC 107-2A and asks for the last E, answer Eating. If it quotes the Pilot's Handbook or AIM 8-1-1, answer Emotion. The S and F in front of that E stay Stress and Fatigue either way.
The trap
The letter trap offers Sleep and Focus, or Stress and Fear. The keyed pair is Stress and Fatigue, because that pair is the same on both FAA lists. Do not "fix" the last E by pretending Emotion and Eating are one idea.
The fatigue trap offers caffeine as a cure, or treats fatigue as a night-only problem. Rest is the remedy. Judgment and reaction time are what fatigue degrades.
The vision trap tells you to stare at the expected point, or to look at a bright light first. Off-center viewing is the keyed technique for detecting a dim object.
Run the checklist items on the free practice test. The fitness lessons in the course keep the two spellings of the final E side by side so you can match the source the question cites.