I was not trying to start a semantic discussion about what constitutes "research." I was trying to point out that location, and the applicable local laws are very different from place to place, even if you "have the right to defend yourself."
Lets look at some situations in the US, as I am more familiar with US law. This is to demonstrate why it is important to know the law. Lets start by saying that everywhere in the US you have the "right to defend yourself."
1. You are in your own house, an unknown person is in your house with a knife in his hand. Can you shoot him? In many states, you must retreat to the bedroom first and can only shoot him if he follows. In some cities you may have to prove that your gun was unloaded, locked up and possibly disassembled. Not to many years ago, in some places in the US, it would be a problem that you even had a gun in the house. In some states, there is a thing called Castle Doctrine, which means you could shoot him, without retreating.
2. In this situation, the guy is on your property, coming to the door, but not inside, with his knife in hand. Can you shoot him? If you live in a state where you must retreat... see above. If your state has Castle Doctrine, does your Castle extend to your property, outside the walls of your house? These are differences, depending on how your version of Castle Doctrine is written.
3. In this situation, the guy is on your property, stealing your car, no knife this time. Can you shoot him? In addition to the above, does your state allow you to use deadly force to protect property? Some do, some do not.
4. In this situation, you are in a public place, legally carrying a CCW. You see an unknown guy, with a knife in his hand. Can you shoot him? Even to protect life, in some places you must retreat first. Even in some states that have Castle Doctrine, that would only apply to your house. Does your state have Stand your Ground, meaning you would not have to retreat first, outside your home? If you were in your car, and you are being car jacked at gun point, does Castle doctrine extend to your car? Or do you need Stand your Ground? Or do you need to let him throw you out of the car first? At that point can you shoot him to protect your property? Different states, different cities, different answers.
Even in one country, the US, you cannot make a blanket statement about when you can use force.
Further, you need to know what "self defense" means legally. In many places, it is legally defined, and has consequences. If you are in a fight and someone wants to charge you with assault, the burden of proof is on the prosecutor. Under certain legal definitions of "self defense" when you claim that, you are confessing to the assault, but saying there are circumstances that apply, making your illegal action, legal. It would be good to know what those where. Also, it shifts the burden of proof to you, the defendant. You are no longer innocent until proven guilty, you just confessed to being guilty, and now you have the burden of proof to show you met the circumstances. These can and do differ, place to place.
Yes, you can defend yourself. But, you need to know the local laws that will be applied. It can get quite messy and very particular. What is important is that you know them, whether or not you have to "research" to gain that knowledge or not.