The word "luck" doesn't appear in the English language until the 1480s, likely borrowed from the Middle High German word "gelücke". Luck as an English word was likely brought into the language as a gambling term but has since developed into a superstitious belief and supernatural phenomenon that various cultures believe in.
Luck can be broken down into two things: the belief that defines the experience of improbable events by chance and an attribute of a person or object. Luck isn't something that is usually measured. It's simply good or bad, and it just is. While luck isn't usually measured, there are superstitious beliefs regarding what may attract good and bad luck. There are also various practices in folk magic that are said to protect, benefit, and ruin one's luck.
The thing about luck that makes it unpredictable is that it doesn't care how good of a person you are (or how good you think you are). Bad luck comes for everybody, whether by improbable chance or by consequence of your own actions. It doesn't judge you or anybody else. You could be one of the most generous and kind individuals out there, and bad luck would still find a way to you.
It is important to mention that there are no universal rules or "correct" beliefs regarding luck. Many cultures believe in the concept of luck but have different beliefs regarding what is lucky and unlucky. One example of this is how many Christian-influenced cultures believe that 7 is a lucky number. At the same time, some Asian cultures believe the number 7 is unlucky.
Another important point to mention is luck is not karma, so avoid treating it like karma. Karma is a doctrine from Hinduism, Buddhism, and Jainism. Luck is a superstitious belief and supernatural phenomenon that many people, regardless of their religon or lack of, believe in. I won't get into the details of karma here because that would derail the entire post. Find a Hindu, Buddhist, or Jain to talk to. Research it on your own time.
The Importance of Luck in Folk Belief
You have to consider how the times were prior to today's conveniences; those conveniences being the internet, cell phones, fast transportation, and many other technologies. For many rural communities, the nearest doctor could easily be a day-long trip or longer away on horseback. If one person had an infected wound or got sick, it could mean death. If the man of the house lost his job, it could mean the entire family starves. If the family didn't starve, the bank may take the house due to them failing to pay their taxes or failing to pay off their loans.
The smallest mistake could come with a heavy price back then. Due to this, people sought to preserve their good luck however they could. As long as their luck was good, they could at least get by.
While we have many conveniences in today's age (I'll admit, conveniences that are often privileges), you still never really know when things are going to go sour. There are still many rural communities and low-income communities where people are living paycheck-to-paycheck. Many of these people have vehicles that are hanging on by a thread because they can't afford anything too new. Many can't afford health insurance or an emergency hospital bill. I could list a number of things, but you get my point. For many people, despite today's conveniences, life is still full of struggle for many. This goes back to what I said earlier- many people still believe that as long as they can keep their luck good, they can at least get by.
I will give the disclaimer now: I'm speaking from the perspective of a person raised in the deep south and currently living in rural appalachia. Some of these are superstitions I grew up with, and some are ones I learned as I grew older. You may be from a place where the beliefs are the opposite of what I have listed here. That's okay. Sometimes, things are different based on location and culture. Take that into account as you read from here.
• Hang horseshoes above the front door facing upwards to keep the good luck from running out.
• Sprinkle cornmeal at the bottom of your savings jar to keep your coins and cash off the hard bottom, that way you'll be kept off hard times.
• If you find a penny facing heads-up, put it in your right shoe for good luck.
• Never burn pine, cedar, dogwood, or sassafras inside. It brings bad luck. (Also, pine will spit like none other so just don't burn it inside so you won't burn your house down.)
• Always exit a building the same way you entered, otherwise you will attract bad luck.
• When you move into a new house, leave your old broom behind. Otherwise you will bring all the negativity from the old house with you.
• Carrying a rabbit's foot attracts good luck.