Is it worth investing a lot of time and money to protect yourself from well-known potential dangers?

For example, the way a criminal strikes a victim is usually in an unjust way. They may strike you from behind, or secretly [a thief], or they may outnumber you with more manpower [gangs] and so on.

Considering this information and the potential dangers of ending up a victim one day, is it really worth it for one to spend a lot of time and money to practice martial arts, firearms or other weapons for self-defense? One practices from early childhood to adulthood training to protect himself only one day to find himself getting randomly stabbed in the back or ganged up on.

Isn’t there way too much injustice in the world to bother yourself with personal protection? Or is it still worth it?