you keep second guessing yourself. It’s Brahms, 100% for sure. But wait I don’t listen to much Brahms and it’s so familiar. Is it Mahler? No, it’s Brahms. But wait… that was just a hair Beethoven? But no it overall doesn’t sound like Beethoven, a bit too modern. Mahler??? No, Brahms1
In retrospect, bouncing back and forth between Beethoven and Mahler as the other two candidates should have told me for sure I was listening to Brahms. Hindsight, etc.