I don't understand not considering tweaking your resume for each application. I could write a novel on what I've done in the last year - how do I narrow that do

I don't understand not considering tweaking your resume for each application. I could write a novel on what I've done in the last year - how do I narrow that down for a resume? I can't buy into the idea that I could write 5ish bullet points today and think it would be the best way for me to represent myself to every position I might apply for. I don't know what proof you need this is useful - you're selling yourself, so make sure to sell what they're trying to buy.