I don't like them hard and fast

Rules I mean. I don't like hard and fast rules. Once made and set in stone they are don't always work for every situation. The GM is now restricted on what they can do. Take shields for example. In most versions of D&D they grant a bonus of one to your armour class. But what about shield size? Larger ones should be better and smaller ones not as good. And if you are surprised, say you don't get your shield up in time. Or you attacked from the rear. Also I don't think a large boulder the size of a sedan hurled by a Giant would give a shield a chance of protecting you. Can they block a magic based attack? What about what they are made of? Are metal ones better than wood? Do shields wear out and you have to replace them? Now the GM needs a whole bunch of rules to cover all that. In my game they add to your AC but they do more to protect you. How the players will ask? Well depends on the situation I say back. I will judge it as necessary. Hmm... funny remember when Game Masters were called Judges? Players want hard and fast rules do be defined so they don't get screwed by them. They want to know exactly how much each thing will affect their character.They want to be in control. But they shouldn't feel threatened by a GM ruling off the cuff. Its not the job of the GM to kill characters. I give the benefit of doubt to the players and assume they don't take risks with their characters unless specifically stated by the players. It still might make some players uncomfortable not knowing the exact odds of everything. But not everything in the world should be revealed to them. Knowing the players intentions is important for determining the outcome not just some hard and fast rule.