Many people like to have fish for pets because they are low maintenance, and can be very relaxing to watch them swim. Most first time fish enthusiast like to keep cold water fish, because they are cheap and most of the different types of these fish will get along together. These fish have some bright colors and have some very fancy fins, but they are mostly large goldfish, and eventually switch to tropical fish to get a larger selection of fish. But keeping tropical fish can be a bit of a gamble, the fish cost more and some of them are very aggressive and will eat your other fish.
There are more different types of tropical fish for you to choose from, and they have a larger variety of colors then cold water fish and keeping them in an aquarium together with other tropical fish does not have to be a gamble, it is not like a trip to the casino to play blackjack, if you do things right there is no gambling involved at all.
The first thing you need to do is some reading before purchasing any fish for your tank. Reading about fish will give you an idea of what species of fish eat other fish, and which ones do not. It will also let you know which meat eating fish will live with what other fish, and make it less of a gamble that you are just buying one fish an expensive meal.
Cichlids are a type of fish that eat other fish but they are a school fish and prefer to be in a tank with other Cichlids, but you want all the other Cichlids to be about the same size, or one day you will come home from a day of playing the most Popular Casino Games in the casino to find several fish missing and one fat fish swimming around slowly.
Cichlids are a surface to medium depth fish. This means they will swim on the top and middle of the tank and will generally not go to the bottom of the tank for very long.
So many people with Cichlids will get a bottom swimmer to fill the tank out. A very popular type of bottom swimmers is catfish. There are many different fish in the species of catfish. Some of these fish are non aggressive and do not get very big, but a fish like this may not be aggressive enough to be in a tank of Cichlids.
You may want to get a more aggressive type of catfish, but if you get a large one it will surely eat the Cichlids, but if it too small you are gambling that the Cichlids will not pick its eyes out.

Just remember that no matter how much you read each fish does have a personality of their own and no matter how much you read that one fish will be friendly with another it putting them in an Aquarium together is gambling.
There is always the possibility that some of your fish will get eaten, but the only way to make keeping fish not a gamble is to keep each fish in their own separate fish tank in the hope that this will keep them all safe, but this will not make for happy fish. With trial and error you will learn what can live with what types of fish and save the gambling for Las Vegas casinos.