The majority of people in this country enjoy having a pet (or a few pets) in their lives. They certainly provide unconditional love, are a good reason to get out & exercise (walking, running, playing "fetch", etc) for us as well as for them, and there's a lot to be said for a cat quietly napping in ones lap as we read, watch TV, or are otherwise occupied. Most people think of their pets as members of their family & make sure that they get the nutrition, medical care, and fun/exercise that they need.
Unfortunately, some people don't think things all the way through before adopting a dog or cat (or bird, reptile, rabbit, etc). They don't know what they're "getting into" when they bring home their new family member, and that can turn into problems for everyone, especially the animal.
Before bringing home a pet, it is a good idea to take into consideration everything that will be required of you for the entire life of that animal; this can often be over 12 or 15 years (or longer!) for many pet dogs & cats. So, if your life isn't stable enough to be sure you'll be able to provide the appropriate amount of time & care into the daily needs of the pet, maybe it's not the right time to impulsively adopt that cute little puppy or kitten. If you need to move to a new living situation, will the pet be allowed there? If you get a different job, will you still have the time each day to make sure your pet isn't left alone for long periods of time (this is especially true with young puppies/kittens) ? If you move in with a new roommate or spouse, will they like the idea of your pet also moving in? Are they allergic to dogs and/or cats? If they already have a pet, will your pet get along with their pet?
Another thing to consider before adopting a pet (this mainly applies to dogs) is what breed of dog you'd like to have. Do some reading or talk with a veterinarian or dog trainer about the typical characteristics of certain breeds. For example, various breeds of herding dogs (Australian Shepards, Border Collies) usually have a LOT of energy and will need a LOT of exercise on a regular basis (usually daily) or else they might find other, undesirable ways to use that energy---like chewing up the furniture or digging holes in the backyard. On the other hand, if you want a dog who you can take jogging with you every day, a small dachshund probably would NOT be your best choice. Doing some "research" about the breed(s) you're interested in makes a lot of sense before you add the dog to your family. If you have a baby or young children, you'll want to make sure you choose a breed that's known for a good temperament, such as Labrador Retriever or a Golden Retriever (but keep in mind that those breeds need regular exercise).
If daily exercise doesn't fit your lifestyle, you might want to get a "lap dog", such as a Shih Tsu or a Lhasa Apso, which don't usually demand much exercise and are content to just go for walks around the neighborhood, or even just some time in the backyard. But don't be fooled into thinking that all small dogs are low-maintenance. Little Jack Russell Terriers are HIGH energy dogs and will not be happy just sitting around the house.
If the idea of ANY kind of daily walks or exercise with your pet seems like it won't fit into your lifestyle, maybe you'd be better off choosing a cat as your companion. They don't need to be walked, they're playful & will interact with you if you use appropriate toys, and they use a litter box so you don't even have to leave the house with them. Once again, however, it's important to make sure that no one in your household is allergic to cats. Too many pets are turned in at animal shelters because the person didn't realize they were allergic to them.
Some people prefer what are called "exotic" pets, such as snakes, lizards & such. These are usually not the type of pets you'd call "warm & cuddly", but they can definitely be interesting as long as you know how to raise them properly---nutrition requirements, heat sources, enclosures that are the proper size, and hopefully a veterinarian nearby who treats that species; not all vets are familiar with exotic pets, or don't want to work with them.
There are SO many other choices that would be good matches for certain people/households---hamsters, rabbits, tropical fish. It's up to you to decide, BEFORE you bring one home, which would be the right one for you. Too often, otherwise wonderful pets end up turned in to animal shelters (or worse, just "dumped" by the side of the road) when a person realizes that it's "just not working out". Those animals don't deserve to be abandoned with the possibility of being euthanized (killed humanely) if no one adopts them; they didn't do anything wrong. It's up to us humans, the ones with the more evolved brains, to make the right choices when it comes to adding a pet to our lives. Maybe that means waiting until you graduate from college & are settled into a home where you'll be sure the pet is welcome & you can devote the time necessary to give that pet a good life. And be sure that you can afford the veterinary care & the feeding of whichever pet you choose.
So do your research before making a decision that you'll be living with for several years, in many cases. Some parrots can live to be over 60 or 70 years old! If you can't devote the time & energy into the proper care of a pet, please don't adopt one at all. It's just not fair to that animal, who deserves a loving home where it will be well cared for...for its entire life.