What actually slows your PC down the most — background apps, storage, or something else?

Genuinely curious what people here deal with day to day. Is it:

• Too many apps fighting for CPU/RAM in the background
• Startup bloat
• An overloaded desktop/window setup (20 windows open, no order)
• Something else entirely

Drop what you've tried to fix it and whether it actually worked. Trying to get a sense of the most common pain point before we do a deeper guide on it.