In chapter 4 of The Lightning Thief, Percy faces physical challenges on top of dealing with an onset of emotional turmoil. He now knows that the people around him have been lying to him and there are monsters trying to end his life. He has a lot of questions but the immediate danger of the Minotaur makes answering them now impossible. All the group can really do is run, because this is one of the tougher monsters that could have come after them.

While Percy is ready to run at first, Grover and his mother being in danger quickly changes his flight response to a fight response. It is ultimately his mother's heroic sacrifice that enrages Percy to the point of being able to kill the Minotaur. Granted, it was ultimately as much luck as planning that saved him.

Percy gets injured during this fight, and as soon as it's over, he breaks emotionally. His mother is gone. All he can do at this point is cry and drag Grover to safety, which he barely manages to do before his head injury catches up with him and he passes out.

In chapter 4, Percy faces a few different trials. One is an existential trial, in which he must come to terms with the fact that his life has been a charade, and the other is a life-or-death challenge in facing the minotaur. Percy doesn’t really contend with the full weight of the existential trial in chapter 4. He does defeat the minotaur, though only momentarily, through a physical battle.

Percy is confused at the start of chapter 4. He sees that his friend Grover isn’t disabled, he learns that he is a demigod, and he finds out that most of his life has been a ploy to keep him safe from Zeus and Hades. If that wasn’t enough to send his head spinning, he learns that he is being tracked by a monster bent on sending him the underworld. The entire thing puts Percy in a daze, and he doesn’t fully realize the implications of everything until much later in the book. This challenge is an ongoing one.

The challenge of the minotaur is one that confronts Percy immediately. Their car ends up being flipped, and Percy has to face the minotaur after it grabs his mom and sends her to Hades. Percy uses his red jacket like a matador and ends up jumping on the monster’s back as it charges at him. He breaks one of the minotaur’s horns when he falls off the beast. That horn is his only weapon, and when it charges at him, he uses it to spear the minotaur in the chest and kill it (though, we learn, only temporarily). Percy then passes out and wakes up in the safety of Camp Halfblood.

Chapter 4 begins with Percy, his mother, and Grover in the car. Percy knows his mother is trying desperately to escape something, but he does not yet know what. The first challenge Percy faces in this chapter is a mental challenge. He discovers that his best friend is part goat and that his job is to "keep tabs" on Percy. Percy must accept that what he believes to be myths are in fact real. In addition, Percy learns that the reason behind these strange occurrences is that someone wants him dead.

After crashing into a ditch, Percy soon learns that something is running towards him. Percy's next challenge in the chapter is a physical one. After escaping the car, Percy, his mother, and Grover must run from a huge figure. Percy soon discovers that what he must escape from is the Minotaur. The Minotaur charges and misses Percy on its first attempt. Percy then sees the monster grab his mother, causing her to turn to mist and making her vanish. Using skills he did not know he possessed, Percy is able to defeat the Minotaur by stabbing it with its own horn. He then carries Grover to safety before losing consciousness.

The first, and most obviously physical, challenge that Percy faces is escaping the Minotaur, a creature which is half man and half bull who wants to catch Percy and kill him.  The Minotaur chases the Camaro driven by his mother that also contains Percy and Grover, his best friend and a satyr who has been protecting him for some time.  Percy successfully escapes the Minotaur, but his mother does not, and he struggles to decide between staying to helping her and running away, as she has ordered him to do.

He also deals with the mental challenges of grappling with a lot of new information: bits and snippets about his father and how much that father knew about him, the fact that he discovers his best friend is part goat, and the knowledge that, in order to be safe, his mother says that he has to go somewhere that his father (who he's angry at for running out on his mother and creating a situation wherein she feels it necessary to marry Gabe, Percy's abusive and stinky stepfather) wanted him to go but she did not.