Cooley's Looking Glass Self
When Buzz Lightyear becomes another toy in Andy's collection, Woody has quite a bit of trouble getting comfortable with this new toy. One of Woody's biggest problem is that Buzz thinks he is a real space ranger. According to Cooley's looking glass self principle, "The feedback we receive from others helps shape our identities."(1) Many of the toys help Buzz with his spaceship and are amazed by his ability to fly. These factors only help Buzz as he continues to believe he is a space ranger because of the feedback he receives from the other toys.
Self Expansion Theory
In Toy Story 3, the audience finds Andy packing up his bags and heading to college. The toys are faced with an incredibly difficult situation. The toys have to decide whether to stay in Andy's attic or to move onto newer and greater places. When the toys and Andy choose to part, the audience is left heartbroken. But, according to the self expansion theory, "People enter into relationships with the opportunity to expand their identities. Successful relationships are a product of the expansion of both parties."(2) In this case, choosing to part was something that had to be done for both Andy and the toys to expand, move on, and have successful relationships in other places.
See Notes for citations and pictures L and M.