Your "self" isn't immutable. You aren't "a certain type of person". You are an evolving experiment. One that is certainly affected by the observer, and one whose outcome is affected by the inputs. If you want to carry something different in your heart, you can do that. You just have to want it bad enough that you can let go of the person you have been.
We are all recovering. Relapse is part of recovery. In everything that you want to improve, on every personal hill that you are climbing, you will eventually backslide. Hopefully you don't tumble all the way down the hill. Hopefully you slide to a stop and immediately refocus on the summit that inspired you in the first place.
And so, why struggle, why strive, when "none of it really matters anyway" ?
I think it is because you have to try, for it to matter.
Maybe it is the historical "fish struggling up onto the land" inside of us, that makes us need struggle or maybe it goes back further than that... Entropy is increasing, everything is falling apart, but life wants to try to pull order from the chaos. Life needs to feel like it is capable of pulling order from the chaos.
Striving, struggling, trying, scraping, any synonym for grappling... MAKES IT MATTER.