In my universe, as it seems in many others, people are simply born with them. It seems to some extent to be hereditary. Generally these powers are portrayed by those who wield them as an ability to access an omnipresent energy the rest of us cannot feel, rather than simply a power residing in themselves. We have no choice but to take their word for it.
And if anyone had ever found a practical means to suppress that ability, I'd have employed it in a heartbeat. Less.