Deku may care for many people in My Hero Academia, but he sometimes loses himself in the process. The ninth wielder of the OFA Quirk has to shoulder many responsibilities in the series. Deku always feels the need to protect everybody around him.
When he was still a Quirkless boy, he felt the need to jump right in and save Bakugo from a Sludge Villain. Unfortunately, he often pushes himself past his physical and mental limits.
His greatest strength is also a major weakness in My Hero Academia. During his worst moments, Deku is too neglectful of his own needs. Luckily, he eventually does climb out of the hole he dug himself into.
Disclaimer: This article contains major spoilers from the My Hero Academia manga.
Deku's best and worst aspect in My Hero Academia is a lack of self preservation
Deku sometimes puts himself through too much pain
This was more of a serious issue during the early days of My Hero Academia. Back when he was still mastering the OFA Quirk, Deku would focus all that energy on a single body part. More often than not, he would severely injure himself.
Deku is more than willing to break every bone in his body. The best example involves the Sports Festival match against Shoto Todoroki. Deku wasn't content with just breaking his fingers once. He broke them several times so that he could get Shoto to use his full power.
While he did get what he wanted, it came at a cost. Deku still carries scars from that encounter. He was even warned that similar injuries could permanently keep him on the shelf.
He also has a borderline hero complex
Deku never misses a chance to run straight into danger. Sometimes it works to his favor, such as when he saved Kota from Muscular in the Forest Training Camp arc. However, this hero complex puts a heavy burden on him.
In fact, this is what All Might was concerned about during the Tartarus Escapees arc. Deku had recently unlocked the Danger Sense Quirk from the fourth OFA user. Naturally, he spent a lot of time looking for criminals without resting. Deku was too focused on looking after other people instead of himself.
It got so bad that Class 1-A had to go after him. Deku felt he needed to run away from his friends and family to protect them from Shigaraki/AFO. Sadly, he never thinks of himself in these situations in My Hero Academia.
Over time, he does learn to control himself better
My Hero Academia gives viewers a lesson in learning from one's mistakes. Slowly but surely, Deku accepts that his body does have limitations. That's why he sought advice from Gran Torino. By learning the Full Cowling technique, Deku could finally channel power in a proper way instead of hurting himself.
However, progress doesn't always move in a linear fashion. There are times when Deku regresses to his worst impulses, such as the Tartarus Escapees arc. Of course, this had more to do with his deteriorating mental state. Keep in mind that Shigaraki/AFO were going after him.
Sometimes even a hero needs saving from themselves. With the support of Class 1-A behind him, Deku eventually realized that he couldn't do everything alone. There is no longer a need to fight these battles alone in My Hero Academia. His classmates reassured him that everything would be okay.