The events of nature are delightfully predictable. The sun rises each morning and warms the earth. Gravity holds everything in place. Spring follows winter. Plants and animals reproduce.
Nature is governed by laws that all contribute to making the world a beautiful place.
When we plant acorns, we get oak trees. When we plant corn, we get more corn - never peas or carrots. The same reasoning works in reverse. If we plant a seed we don't recognize and an oaks grows from it, we know for certain that what we planted was an acorn. We understand and accept all this when it's about seeds, but it seems to surprise us in other areas of life, like our own feelings and behavior.