And why didn't he explain to Sean (He seemed as if he was about to, but got sidetracked).
Throwing out a present like that, which would have meant a lot to someone in his position, seemed completely out of character.
If he had completely finished with "Life", it might have made some sense, but he was still prepared to go to enormous lengths to find Sean, so it clearly wasn't a final "closing the chapter" moment.
Because he HAD given up at that point. He had literally given up on "Life" and fate in every way possible. Seemed very clear, especially metaphorically.
shareIt may have seemed clear to you - I assume you didn't even read the second and third paragraph.
And, maybe you just glossed over the fact that out of all the "Life" related things that he could have got rid of, he chose something that was not only of immediate, practical, use but probably the only thing he'd been given from all the time he worked there by someone who was indicating that he was valued and appreciated.
So, superficially, yes, you could say it was obvious, but dig a bit deeper and it's a puzzle.
And even your very superficial reasoning does not explain why he didn't, when he had the opportunity, explain his action to someone to whom he must have known he had behaved in a hurtful manner - especially after the enormous effort he had made to find him.
I admit that felt more like a plot device to me than realistic, and throwing away something one turns out to really need seems to be a common movie trope. However, one could make an argument for why he might. At that moment it wasn't a symbol of all his hard work and successes, but of this one final failure at that job despite the lengths he went to in order to try to come through. It was an irrational overreaction, but goodness knows humans do that sometimes.
"The men people admire are daring liars; those they most detest are men who speak the truth"
I agree with you about "an irrational overreaction." It was a moment of peevishness and of course it was necessary to the story.
shareIt was a reminder of Sean and Life. When he threw away the wallet, he had been fired and hit a wall with the hunt for #25, so he felt like quitting. So he, threw away the wallet. He had quit.
Right after that, he sits down and takes a look at the curved object with a chip. He realizes its his mother's piano, and then continues the hunt for the negative.