I think as soon as one realizes they are unable to focus on the task at hand.
Once a person sees they can no longer function because they have no control over their thoughts or emotions it’s time to seek help.
Some people are great at hiding their issues or faking things are fine but no one can hide from his or herself. People change when THEY want to change. Life is a personal journey and each of has "free will" to make our own decisions.
It takes "energy" to make changes and it's difficult to muster it up especially if you are depressed. Very similar to assembling a 1000 piece puzzle you have to start off putting together the corners and working your way inward. Thinking in terms of the overall goal can seem very daunting. One must break things down.
How do you eat an elephant? "One bite at a time"