New shoes are like new friends, they have to be worn in.
The answer might be one of the following:
A. The shoes was too attractive, you bought it even if it is the wrong size/ it doesn't FIT you
B. You have an anomaly in you bone/ feet structure that's why you have difficulty wearing normal shoes
C. Your not used to wear such kind of shoes
D. If you want a technical answer then here it goes: The shoes and your feet are not yet adapted thus the elasticity of the material is still on the original shape and form and for that reason it brings discomfort on your lower appendages. Given a week, your feet will learn to adapt to its new "house" while at the same time due to the principle of use,tear and memory in materials, your shoes starts to loosen especially on the heel part and slowly accommodate to the shape width and bone structures of your feet/foot.
Hope you have find the correct answer for your common question.
They shouldn't so either you've bought the wrong size or, in the case of stiffened shoes (hiking boots), you've not worn them in or you need to wear a better pair of socks.
There is another possibility... you may be like me and have one foot which is half a size larger than the other, get your feet measured again by someone who knows what they are doing.
Because your feet are too damn big for them!
because god DOES have a sense of humor lol :D