The Lightning Thief
How we cite our quotes:
I felt so relieved, I wanted to cry, though I didn't think that would be very heroic. Grover was the only friend I'd ever had for longer than a few months. I wasn't sure what good a satyr could do against the forces of the dead, but I felt better knowing he'd be with me. (9.192)
Percy loves Grover, and he loves him for the kind of person (or satyr) he is. He doesn't care that Grover isn't the most ferocious protector on the planet; Percy just wants a great friend along for the ride. Rather than worry about status and about belonging to the right group of friends (like many twelve-year-olds are), Percy cares more about being with people he truly likes.
"Your mom stayed with him to protect you. She was a smart lady. She must've loved you a lot to put up with that guy—if that makes you feel any better." (10.100)
One of Sally Jackson's greatest sacrifices for Percy is marrying and living with Smelly Gabe. When Grover tells Percy this, we realize that everything Sally does is for Percy.
The truth was I didn't care about retrieving Zeus's lightning bolt, or saving the world, or even helping my father out of trouble.
All I cared about was my mom. Hades had taken her unfairly, and Hades was going to give her back. (10.103-104)
One could say that Percy embarks upon his quest out of love for his mother. He is never once tempted to keep the master bolt for himself. His love for his mother helps him keep focused and keep his priorities straight. While even gods succumb to temptation (like Ares at the thought of starting World War III), Percy seems almost immune.