Answer:
It is often necessary to start campfire with many pieces of kindling rather than large logs because it is easier to ignite smaller pieces than larger pieces. Imagine wanting to light up a pile of clothes and a small piece of a shirt. Which ignites faster? The piece of a shirt, because it is smaller and more likely to burn very quickly. Additionally, people criss-cross these tiny pieces of wood to enable more surface area and to allow more oxygen to pass through. As you know, oxygen is necessary for a flame to ignite.