All Might was the first Symbol of Peace in the My Hero Academia universe and the example that Izuku Midoriya aspired to take after. He once served as Japan's greatest protector, having been personally responsible for ending All For One's reign of terror.
In spite of the impression Toshinori has on many, his confident and smiling veneer belies many debilitating weaknesses both in regard to his capacity for protecting others and as well as personal character flaws. Through identifying All Might's greatest qualities and contrasting them against his worst, we can better understand whether or not hero society is as secure as it seems.
10 WEAKNESS: He Wasn't Able To Teach Midoriya What He Needed To Know About One For All
Although All Might was Midoriya's primary mentor in teaching the tenants of One For All, he wasn't proficient at passing on his quirk's secrets to his successor. Since Deku was constantly being hospitalized by applying his power (much to Recovery Girl's chagrin and anxiety), Gran Torino had to step in and teach him the finer points of his new abilities.
Despite his appalling shortcomings as an educator, Toshinori was still able to impart the shoot style onto his student.
9 STRENGTH: All Might Has Reliably Strong Character Judgment
All Might is a fantastic judge of character, as evinced through his decision to impart One For All to Izuku Midoriya rather than the other heroes who came recommended to him by constituents (particularly Sir Nighteye).
Additionally, he understood the source of Bakugo's insecurity and leveled with him, rather than using derision or his rank to corral the flame user back into line. Because of his console, Bakugo and Deku were (mostly) able to put aside their differences and work toward a more productive goal.
8 WEAKNESS: All Might's Endurance Decreases Over Time
After his perilous fight against All For One, Toshinori's ability to use his quirk has been on a steady decline. At the start of the series, he was capable of managing it for three hours a day - by the conclusion of Shigaraki's attack and the battle against the prime nomu, he was only able to manage it for one.
While All Might is capable of going beyond his limit, doing so will reduce his capacity to use his quirk on subsequent missions. His debilitating health was one of the reasons why he pursued a successor so aggressively.
7 STRENGTH: All Might Is The Most Physically Powerful Character In The Series
All Might is handily the strongest character in the series, both in the sense of brute force and combat prowess. He was capable of defeating the prime nomu despite how it was specifically tailored to counter and defeat him.
Additionally, he struck down All For One by himself despite having been severely wounded through one of the criminal kingpin's underhanded tricks. In both instances, he was already at or past his limit by the beginning of the battle but managed to reign victorious anyway.
6 WEAKNESS: All Might's Arsenal Is Extremely Limited
Although All Might's excess of strength renders him a formidable warrior, he has no secondary abilities that would help him win a fight. The impact of his punches will sometimes create shockwaves, though doing so is often unintentional (as contrasted against Midoriya's more deliberate and targeted shoot style).
His necessity for melee combat also renders him vulnerable to particularly deadly melee quirks that can kill targets in a single touch, such as those of Tomura Shigaraki or Kai Chisaki.
5 STRENGTH: All Might's Charisma Has Won Him Dozens Of Reliable Allies
Arguably All Might's greatest strength is his charisma and ability to inspire others. After he reached his limit against the prime nomu during the battle for U.A High, Snipe and the other teachers intervened to save the day.
This allowed him to alleviate much of his burden, especially given the aforementioned restrictions placed on his endurance. It was also sufficient to inspire generations of heroes and deter hundreds of potential evildoers from ever turning their quirks toward more malicious purposes with the intent of personal gain.
4 WEAKNESS: All Might Has Seldom Fought Intelligently
All Might has seldom fought intelligently, instead attempting merely to power through his targets and overwhelm them with physical force. All For One was able to use his shortcoming against him during their battle at Kamino, where he teleported Gran Torino in front of him to purpose as a human shield.
The only instance of Toshinori placing brain over brawn was when he concentrated what remained of One For All into his fist to defeat All For One with a final desperate punch. However, this could equally be attributed to the possibility that he no longer had the strength to maintain his muscle form in its entirety.
3 STRENGTH: All Might Has Legendary Durability
All Might's durability is among his greatest assets and has served him well during his perpetual war against the League of Villains. His torso was so sturdy that Kurogiri couldn't close a warp gate around his waist to decapitate him, requiring time and exertion to make such a tactic possible.
Toshinori was also resilient enough to withstand point-blank explosions to the face from Bakugo and having his own strength turned against him by All For One.
2 WEAKNESS: All Might Recklessly Exhausts His Power
Compelled to heroism whenever evil arises, All Might's recklessness has been his undoing in more than one instance. Since he cannot abide villainy even momentarily, he will often overexert himself when other pros might be available to take his place instead.
His fixation on minor threats leaves him exhausted, a fact that Shigaraki exploited when planning his first attack on U.A. Through littering inconsequential criminals in Toshinori's path on his way to work, he was able to exhaust him and limit the capacity he could unleash One For All against more serious threats.
1 STRENGTH: All Might Has Shown A Fantastic Aptitude For Teamwork
In addition to providing an inspiration to new generations of heroes and an omen to villains worldwide, All Might is fantastic when working in a team. After uncovering the League of Villains' hideout, he collaborated with Gran Torino and Kamui Woods to restrain the evildoers and save his student.
His cooperation would be seen again during the battle at Kamino, where he would work alongside Mt. Lady and Best Jeanist in order to help defeat All For One. Unfortunately, his allies weren't as useful in this instance and were primarily purposed to evacuate bystanders.