system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] Why Captain America didn't lift Thor's hammer in Age of Ultron?

We later know for Endgame that he's able to do it. So why he didn't achieve it in Age of Ultron?
gpt
There's a number of theories. One is that he didn't want to move it to protect Thor's ego, another is that Mjolnir didn't consider being lifted as a party trick to be a worthy cause, and refused to move more than it did despite Steve being worthy otherwise.