- Wrong size: If the planner is too small, there won't be enough writing space. If it's too big, you might not want to carry it around with you.
- Wrong format: For example, it's difficult to do time blocking in a horizontal untimed format, you need vertical timed days. Also, it's difficult to effectively plan ahead in a day per page planner, a weekly format gives a better overview.
- Wrong aesthetics: Maybe you're embarrassed to use it in front of people because of the size or design, maybe you don't like the paper or the cover, maybe the font is annoying to look at. Whatever keeps you from using your planner means it's time for a new one.
Not your planner's fault
- You don't look at it: It's closed. As my sister says, "A closed planner is a dead planner."
- You don't have it: It's in your bag. You left it at work/ on your desk at home/ on the bus. You need to decide on a place in your every location where you can leave your planner open and visible. When I'm working it's open beside me. Otherwise when I'm home it's on a book stand in my kitchen.
- You don't write in it: Figure out why you don't write in it (see You Don't Have It and/ or Wrong Aesthetics). You need to treat your planner as your go-to landing place throughout the day. Keep it with you, keep it open and write in it (and look at it) often. Write your scheduled items, update them when they change, write tentative plans and things to do. One of the Great Planner Truths is, The More You Use It, The More You Use It. It becomes more and more useful the more it's used.