Flies are ecologically important. They pollinate plants. They break down dead things. They are nature’s garbage collectors. But they do not belong in your bedroom while you sleep. That’s a boundary issue. You are allowed to reclaim your space.
Every fly you evict is a victory for sanity and hygiene. Plus, it’s a great party story. “I used a bag of water and a banana to defeat a winged enemy.” You sound like a wizard.
So get out there. Be patient. Be clever. Be the fly’s worst nightmare. And remember: they’re just tiny jerks with wings. You are a human with a plan. You win.