There are a lot of things we ponder in life, like our destinies or the vastness of the universe. Chances are, however, that very few of us wonder too much about boogers. We only give them momentary consideration when they're visibly hanging out of the nose. Beyond that, they escape our notice. But like bats in a cave, they're always hanging around.
There's a very good reason boogers are ubiquitous inhabitants of the nasal cavity: They're signs of a well-guarded respiratory system. A lot of things come into the body through the nose. When we breathe, germs and allergens are ushered in. If everything that entered our noses made it through to our lungs, our breathing organs would have a hard time doing their jobs, which is to process oxygen and release carbon dioxide.
To help ensure the lungs are free to perform unhindered, mucus (what we often refer to as "snot") clings to nasal invaders to stop or slow their progress. Incidentally, this is why our bodies create so much mucus when we have a cold — it's an attempt to keep the virus out of the respiratory system.
Mucus also has another defensive role: to prevent the nasal passage from drying out. If the inside of the nose got too dry and started to crack, it would create another entryway for germs to enter the body. So keeping the nostrils moist is an important task.
While mucus is busy performing these duties, it combines with the material entering the nose, as well as the small hairs, or "cilia," found there. All of those things wad together, and the result is boogers.
As you've probably noticed, not all boogers are the same. For instance, some are sticky, and some are hard. This is often because of how long they've been in the nose. A tough or crusty booger may be older and more dried out than its slimy counterpart.
So, you can expect to frequently come across boogers of varying sizes, textures and consistencies in your nose. Feel free to go back to forgetting they're there. But, if you notice the mucus increases significantly or changes color, it might be a sign you're having an allergic reaction or coming down with something. So keep an eye on it, and call your doctor if you start experiencing other symptoms, like fever.