They often become angry when things do not happen the way they planned.

VOA: special.2009.03.24

Or, they may happen more and more often and become worse.

VOA: special.2009.01.06

Chronic tension headaches happen more often.

VOA: special.2010.03.30

"We recommended hemorrhage drills just like fire drills. For an event that doesn't happen very often, people need to practice.

VOA: standard.2010.06.23

"Something else, which we hope does not happen very often, but which happens from time to time are the accidents which can release huge amounts of chemicals or radioactive-during Chernobyl, the radioactive things.

VOA: standard.2009.03.23