What gives some people a higher pain threshold than others?

Is this due to the toughness of a person, to be able to withstand more pain without making too big a deal of it, or do some people just experience pain differently via. being physically more sensitive to it?

Why is a person with a lower pain threshold considered weaker? Are they really weaker or is their body simply tuned to be more sensitive to pain and hence they experience it differently? Is it completely psychological? Why would one person exposed to what is deemed to be the same level of pain rate it as 4 on a scale of 1–10 while another may rate it much higher?

This question is based on two people being of similar physical condition and overall strength.