Well, I'll share some experiences to give you an idea of what some of the pitfalls have been. My family owns quite a few units.
Cat urine and feces everywhere throughout units.
Smoke literally turning the walls yellow, combining with grease in the kitchen. It took me two days of scrubbing every surface to just make it look ok. We had to toss the AC and carpet, as the smell wouldn't go away.
Unapproved dogs ruining hardwood floors 'they were only here for a weekend'.
Mold growing in a bedroom without the tenant letting us know.
Lots of leaks. It is VERY important to have access to plumbing in rental properties.
People going months without paying rent, but not able to evict.
A person complaining about discrimination because he was attempting to become trans (I had no idea).
Tenants tape recording conversations without permission.
One tenant accused another of rape. They expected us to take action based on the accusation.
Sewer line to a building was clogged. We had to shut the water off to 16 units for two days while it was investigated/replaced. Total cost $45k.
People completely ignore assigned parking and have their friends park wherever they want, despite plenty of street parking.
Many people do not understand that the security deposit is not the last month's rent.
People who owe thousands of dollars to their current landlord literally begging to let them move in.
People who give their friend's phone number as landlord and have them lie over the phone.
People who intentionally damage the property before leaving and try to claim that the property was in that condition when they moved in, and they expect their full security deposit back because it was in such disrepair. They also left condoms in windows between the glass panes.
Many, many calls late at night to complain about noise.
People complaining about asthma being exacerbated because it was too hot (the ac wasn't working too well because of all the smoke in it).
Drugs.
Rental properties can be an excellent source of income if you find the right tenants and treat them well, plan ahead, and are willing and able to do some of the work yourself. Those stories above were nightmares to deal with, and there are many more, but they are definitely the exception, not the rule. Just learn to anticipate problems and save accordingly. Most people don't do that in their lives, so they would not do well as landlords. The return on investment is usually better than the stock market, but a real estate property is not a liquid asset. You need to save for repairs, save for legal fees, save for renovations, save for missed rent, and many other things.