The idea that you can in effect pick up any weapon, be it sword, mace, or dagger, and be able to do damage with it let alone kill an armored and armed opponent. This is regrettably not so. Nor is it so that PC's (player characters) are actually born yesterday. The fact is, if a person is born into a game world destined for PC-dom and all the glory and fame that is associated with it, then chances are they have been doing something with their lives before we get to cart them around.
Enter the Classes!
For the sake of not rambling on and on, or at least not more than I already have, I'll stick with the three Archetypes.
Thief: They usually don't get formal training and their skills are almost always stealth based and are self taught, sometimes trading secrets with other thieves. As a result aren't very good in an out and out fight.
Mage: Years and years of studying the arcane arts under either a single master or in a larger community of mages in an academy or school (no Harry Potter jokes) with other students. Careful study is more important to this class than most others mostly due to the fact that poor ability can often lead to death and worse with even the simplest of spells.
Warrior: Years of training with various weapons and armor usually as part of a militia or mercenary unit or even a full army. Because of their focus on the physical they generally don't study magic and because of the nature of their training they're not very stealthy.
I went through that for the reason that I feel that not having a set of skills at the beginning is not only unrealistic, but also very immersion breaking for me. Now, That said, I am wondering what you think. Do you think the above should matter or are you all for wild sword waving and rampant spellcasting with no "realism"? Also TL : DR?