everthing Rick just said....also...
being right eye dominant helps. hold your arm out with your index finger and thumb touching to make a 'circle'. look through the circle and line up a distant object so it's visible within the circle. close your left eye keeping the right eye open - and vice versa. your dominant eye is the open eye that kept the object in the circle.
If you're your left eye dominant - you won't be for long if you continue to hold the viewfinder up to your right eye. you'll find yourself with a glazed half open left eye in no time
I'll bet that there's loads of people on this forum with a droopy left eyelid as a result of decades of shooting (myself included).
It's why I maintain that Paris Hilton, Forest Whittaker, Thom Yorke etc all must be amateur photographers