When the thread tension’s off, the stitch looks fine on top and like chaos underneath. Check the back of your work.

Looking fine on the surface is not the same as being right. With the tension off, the top of the stitch gives nothing away while the underside is a tangle, and you only learn which you have by turning it over. Plenty of work hides its problems on the side you are not facing. Checking the back is a habit rather than an instinct.

Turn something over this week before you call it finished. Reread the question you actually answered, check the second page, look again at the step you skipped. Finding it yourself is far cheaper than having it found for you.