During your marriage, you probably didn't have a written agreement with your spouse regarding how you would divide the parenting duties. You just naturally fell into taking care of certain things when it came to the children. For example, you may have been the primary breadwinner while your spouse took care of a large portion of the children's daily needs and activities.
This does not mean that, now that you are going through a divorce, you must relegate yourself to paying child support and spending less time with the children than the other parent. During your divorce, you can work out a parenting plan that provides each of you with a more equitable division of time with the children.