I don't think the parent's advice is anything to do with "just try harder"...I think he's saying that we try to create habits for things we don't really care about...just stuff we think we should do for productivity or health or whatever.

You don't need to 'try harder'; you need to question your motivation for the habit in the first place. Either a thought will click that clarifies why a habit is actually important, or you'll realise you are pressuring yourself to take on a habit that doesn't really matter to you (when you strip away the bullshit)

edit: and if the importance finally clicks for you, you'll generally just start working on the habit. I struggled with weight for years, and then eventually motivation/understanding clicked and I lost 6stone/40kg/90lb in around 18 months (and have lost a little more since, and kept it off for years).