I finally had a chance to see [the 2007 movie] “I Am Legend“, and analyzed it as a writer, and from a technical perspective.
I’ve seen a lot of discussion over his [use of a] M4  [Carbine as his primary weapon]. I have to say for that type of fighting, I’d prefer a shotgun. However, a shotgun doesn’t reload fast enough. He might be better off with a good .308 self-loading carbine, if he can find adequate soft-point ammo. In New York City, that’s unlikely. National Guard armories would only have ball ammo, and likely wouldn’t have anything other than standard duty weapons. Add in that he was likely at least familiarized with the M4 as a military surgeon and officer, I think the M4 was about the best practical choice under the circumstances, though inadequate. Lesson: Obviously, for those preparing for any of various disasters, this is a reminder to plan ahead.
Much is made of his OPSEC , including bleaching his footsteps to kill scents. What isn’t discussed is how he hides the scent of fuel for his generators, or the exhaust smell. Also, this is supposed to be three years after the disaster struck. How does he hide his tracks in winter, with snow? This would likely necessitate long stays inside. Lesson: Obviously, that would mean more preparations. You may have to bunker down due to weather or other events.
The steel shutters and reinforcements on the building don’t extend above the ground floor. This is an obvious failure point. His armory also should not have been in one closet, but in multiple locations, possibly the central stairwell, on each floor. Lesson: A point source failure of any resource–food, weapons, water, medicine, fuel–can kill you. Diversify your preparations.
One of the character’s critical intel flaws is failing to note that: he and the “Dark seekers” have overlapping territories, and their search methods are as precise and professional as his. We see him searching a building that has already been stripped of food, but there is no extraneous damage or vandalism. This was a key item that his enemy were not mindless and irrational, but rather very organized and intelligent. There are other events that indicate this, and he missed them, too. Obviously, he was emotionally reluctant to consider human attributes remaining in people so sick and damaged. Never underestimate your opponent, and always remember that from his point of view, he is correct and you are in the wrong. It may not be possible to understand his point of view, but the attempt must be made.
There are several signs that his own rationality is slipping. Obviously, talking to mannequins and creating scenes with them is a coping mechanism. However, herding deer with a sports car and attempting to take potshots might be a thrill, but a dangerous one. Likewise, when he loses Sam, his dog, his vengeful actions almost get him killed for no gain. His character did a great many things to maintain himself–a regular schedule, replaying old news and movies, interaction with his dog, but ultimately, we are a social creature and cannot operate alone. This is also driven home when he is trapped. Consider that other disasters or accidents are possible, too–broken limbs, car failures. Lesson:Plan to be part of a team, with organization and training. Do this before disaster strikes.
Besides the deer, we see lions, presumably escaped from a zoo. We don’t see any transformed wildlife, but knowing dogs and rats did, it’s reasonable to assume others did. This is a massive potential threat. The metabolic issues in this scenario might have meant transformed predators are not viable long term, due to massive food demands, but in the short term, one could create a tremendous amount of damage, or infect an entire herd of deer. In addition, while there are lots of supplies he can loot in the short term, apart from a small garden patch, there is little space for food or material production. Lesson: A city is a consumer, not a producer, of base resources. It is not the place for a long-term base in such a scenario.
Conversely, the character did well by operating from a central location, keeping records and charts, performing regular patrols and intel sweeps, operating in a scientific fashion, attempting to contact others, holding to a regular schedule, acquiring resources, keeping fit, and demonstrating generally good fire discipline and caution. Lesson: Even the best, most prepared individual can make mistakes. Constantly review your scenarios and preparations, and have someone else do so, too. – Michael Z. Williamson