Often, used to
This expression is used to describe something which occurs repeatedly or a person who performs some action repeatedly or regularly.
It is often used together with 곧잘, 자주, 가끔.
The form '-고는 하다' is a variant of this form.
1. Only verbs can come before -곤 하다.
2. Because '-곤 하다' is used to describe something customarily done, similar to a habit, it sounds strange when used to describe something that always happens, without exception.
Class always starts at 9:00, without exception, so -곤 하다 therefore cannot be used.
3. The expression -곤 하다 also cannot be used to describe situations that do not repeat or that continue to a certain degree.
High school graduation normally occurs only once in a person's life, so -곤 하다 cannot be used.
Here, -곤 하다 cannot be used because it is impossible to repeatedly like and then not like a singer as if it were a habitual occurrence during a particular time period.
Here, -곤 하다 cannot be used because it would mean the speaker worked for five years, quit the company, and then repeated the entire process multiple times.
Indicate a habitual action of the present or past.