A psychologist says 4 factors determine whether you're ready to have a kid — but most people focus on just one

It's a piece of wisdom you might have heard in the context of marriage, meaning both partners also need to be committed to weather the inevitable ups and downs of the relationship.

But the adage applies just as well to parenting — which, as it turns out, is something that can sound perfectly sensible but is often hard to internalize.

That's according to Carl Pickhardt, a psychologist who's published multiple books about parenting, including, most recently, "Surviving Your Child's Adolescence."

"The readiness to invest your love and care in this little person" is frequently what makes people feel like they're prepared to be a parent, Pickhardt told Business Insider. "That's usually the great persuader."

Unfortunately, that particular form of readiness is only one of four factors Pickhardt has identified that determine whether you're prepared to have a kid:

1. A solid partnership

If you're planning to raise your child with someone else, Pickhardt said, "you are going to get to know your partner in a way you never got to know them before." In fact, you and your partner will get to know yourselves in entirely new ways.

You'll have new value conflicts, like when the baby's crying in the other room and one of you wants to pick him up and comfort him, while the other thinks it's better to let him be.

"Who's right?" Pickhardt said. Somehow you'll have to resolve the difference. The bottom line is that "the partnership has to support all those changes."

If you're planning to raise your child on your own, Pickhardt said you'll want to create a support network of friends and family. For one thing, you'll feel less isolated during hard times — but you'll also be able to share good times in the child's life.

2. The ability to take care of yourself

Parenting, Pickhardt said, is fundamentally about self-sacrifice. But parents shouldn't "self-sacrifice to the point where they feel the child is tyrannizing their life."

They'll only wind up angry and resentful toward the child, even though it's obviously not the kid's fault.

While it's tempting to make your child the top priority in your life, Pickhardt said the child should actually be a third-order priority. First is your well-being and second is the health of your partnership. If you neglect those, it "makes everybody unhappy sooner or later."

3. Self-discipline

Before you have a kid, Pickhardt said, you need to "have an adequate work ethic in place." You should be able to finish what you start.

It's easy to let the work of parenting deplete you if you're not prepared for the tremendous amount of effort that it involves.

4. A vision of parenting as self-fulfillment

This is that "great persuader" that we mentioned earlier. It's the desire to "see this little child develop into a person," Pickhardt said.

In Pickhardt's experience working with clients, he's found that most people don't think about the first three factors until they already have a child.

Of course, none of this is to say that if you don't achieve all four readiness factors before having a kid, you'll be a terrible parent. You probably won't.

But Pickhardt explained that if you only have that desire for self-fulfillment and that willingness to love, and you aren't prepared in other ways, "you're going to have a hard time raising a child."