Well, familial, relationship or social pressure surely are the wrong reasons to have children. Once you're in, you're in it for the long haul and have to accept the pitfalls and highlights with duty, discipline and commitment, no matter what! I'd say no one knows if he or she is cut out for parenthood beforehand, but people may have weaker or stronger inclinations in either direction based on their own goals, personalities, lifestyles and preferences. Having children means putting your desires, wishes, wants, ambitions and even needs on the backburner, with the understanding that these self-directed objectives may eventually be fulfilled, but doing so will either be delayed, done under duress (time, limited resources, etc.) or perpetually put on hold. For example, I earned my master's degree just last year; it took me a total of nearly four years to complete the program - I went more slowly than I would have had I not had children. But because I did - and since I worked full-time as well - I had to take a measured approach, whereas I am sure I would have been done in two years if I were without children.
Having children places pressure on your finances. They are not inexpensive! I did the math once when we had one, and between childcare, diapers, formula, food, clothing, furniture, doctor's appointments and the bill that was due from the hospital that insurance did not cover, we had invested tens of thousands of dollars by the time she was three. As someone who doesn't want kids, you may think about how you could have used that money - vacations, home improvements, lots of nights on the town, etc. - but as a parent, you can no longer look at it that way.
As a woman, bearing children changes your body, and you have to accept that you may never look exactly the same again without great discipline and hard work - even then, it's still luck of the draw! I worked out during both pregnancies and have been successful in emerging from two pregnancies relatively "unscarred" by the physical toll. But this is only because I have been devoted to wellness and exercise for years, and MADE time for fitness in my life, even with children in tow. I can fit into many of the same clothes I had pre-babies. Some women think it's vain to think in this vein, but it's a reality most women wonder about, even if they don't state it. You have to be prepared for whatever you end up looking like afterwards. And if you don't like it, you have to be committed to working like hell to regain your body.
You also have to be braced for the lifestyle changes you will endure. You will not be able to get up and go when you want to. And you'll realize that all the folks who want grandkids or little cousins or great nieces and nephews are NEVER available to babysit for you. LOL! Many people with children don't get to get out as often as they'd like, and that's because it's hard to find a babysitter who you trust and it's even harder sometimes to find the $8-$14/hour to pay them for a night out with your husband.
I am now more than seven years into my parenting journey, and I must admit that it does go by fast, as cliche as that may sound. In just 11 more years, my older daughter will be graduating from high school and on her way to becoming her own woman. That really is not too far ahead into the future. It seems like I just had her yesterday!
Parenthood has helped me slow down and appreciate the pure normalcy of a typical family life. We eat dinner together; my girls get involved and help me cook in the kitchen; every weekend is a ritual when I'm doing their hair in all sorts of braids and twists; our outings, from local trips to the park or museums to vacations at the beach are precious and priceless; looking at them and seeing them evolve into their own people is an incredible thing. And it's even more so when you see them extolling the values, virtues and knowledge you just hope they'd benefit from.
I could say a lot more! But I am hoping this provides some perspective and balance.