Does wood split if a nail is driven in with out a hole? Does the thickness matter?

All of the above answers are good. But, in this case, size matters. A larger nail is more likely to split the wood than a smaller one.Does wood split if a nail is driven in with out a hole? Does the thickness matter?
if the wood is too dry or the nail too close to the end it can but a pilot hole isn;t usually neededDoes wood split if a nail is driven in with out a hole? Does the thickness matter?
The thickness of the wood matters but also it's density...you should drill oak but pine is soft so you can drive a nail right thru.....when in doubt drill a pilot hole.
an old carpenters trick is to grind flat the point of a nail which will make the nail cut the woods grain rather than spreading it and causing the wood to split. Softer and dryer woods generally are more likely to split