I have severe animal allergies. I used to get really frustrated by people bringing their pets onto the plane. There is generally no way to let the airline know ahead of time that I can't be seated next to an animal, and no guarantee that there will be a place they can relocate me to. Now I always have an n95 mask on me, so it's not a huge deal unless the flight is super long (itchy eyes are still a thing). Wish I had thought of that sooner.