At first glance, the answer to this question seems easy: You adopt because you want a child. But it goes a lot deeper than that. Some people choose to adopt because they can't conceive a biological child and still feel a strong desire to experience parenthood. In many cases, they've tried for years to conceive and explored various fertility treatments but were ultimately unsuccessful. Others want to adopt regardless of whether they can conceive a child. Many adoptive families include both biological and adopted children.
Your motivations behind adoption also go beyond whether you can have a biological child -- adoption isn't for everyone, and there's nothing wrong with that. If you're thinking of adopting because you can't conceive, you'll need to go through the process of grieving that loss first. If you consider adoption to be "second best" to having a biological child, think about how that attitude would make an adoptive child feel. And if you think that adopting will heal a troubled relationship, think about the pressure that you're putting on a child who deserves to have parents who are in a healthy relationship.
These are just a few reasons why you may want to reconsider adoption. However, if you want to adopt because you truly enjoy children and want to be a parent, adoption might be for you.