How do animals become strays?

There are so many different reasons why people's dogs become strays...

• Money, sometimes people cannot afford the vet or their services on treatment and in result sometimes the dog ends up in the shelter or people open their door and let them go in result being picked up by a police officer or neighbor and transfered to the shelter.
• Unrulely behavior, sometimes people do not get the dog proper training, in result the dog may develop aggression problems in food, toys or strangers and owners themselves. These people sometimes "give up" on the dog and it either ends up in the shelter or people let them go on purpose because they cannot train the dog or possibly cannot afford it, some even embaressd by it may let it go so people can't take the blame or are afraid of the law and what consequences the person may face.
• If a dog loses a dog fight, people either kill it or just let it go lucky if we catch the people who commit these heinous crimes.
• If someone is moving to an apartment, house or condo not dog friendly likely some get turned over to shelters the others people leave their animals behind if they get out likely it will hunt for food. in results being picked up by the police or neighbor and turned into the shelter.
• Maybe the dog runs away alot the person will eventually give up and let it run away for good and not call to claim it, therefore the dog gets lost and becomes stray.