A $3 can opener is not the deal it seems to be. This is important. You need to remember this advice when you're living at the Y with no refrigerator and eating lots of canned foods.
"This is a no-brainer," you'll think, when you find the $3 can opener right next to a $15 can opener. You'll congratulate yourself for being such a shopping genius. But I ask that you please, please stop yourself there, remember this post, and buy a quality can opener.
Otherwise you will get your $3 can opener home and discover that it doesn't do its only job, opening cans. You will spend lots of time trying to force the can opener to work, eventually using it to just punch holes in a circle around the lid of the can. Not only will this create dangerous, jagged edges on your cans; it will also break the can opener completely.
And you will feel stupid because you were so smugly self-satisfied when you found the $3 can opener.
And you will have to buy a decent can opener anyway.