In the video for the subdivided boxes, I talk about a problem students will certainly run into - the little inaccuracies that will accumulate as you continue to make estimations which will inevitably be off by a little bit. As explained in the video, you ultimately do have to keep rolling with the punches - adjusting trajectories to get them to line up, to compensate for one another, even though those trajectories aren't perfect.

So, according to what's mentioned in that video, your first box is incorrect, whereas the second box (despite not being perfect) is very well done, and follows the intended approach.

With practice, your spatial reasoning skills will improve to shrink those margins of error. That isn't to say there won't be mistakes, but that they'll be minimal enough to be inconsequential, and at the same time you'll get better at compensating for them to avoid any noticeable issues in the resulting drawings. That said, the drawings you do in this course are all exercises - so there's no such thing as a "ruined drawing". Whether or not it comes out looking good is irrelevant - what matters is what you learned from the process, and one of the many things we learn is to adhere to the marks we've put down in previous phases of construction. Yeah, as you noticed in your first swing at this lesson, you ended up with a lot of wonky boxes - but it is from that point your responsibility to behave as though that box is what you intended, and to work within it, rather than undermining and contradicting it in the pursuit of a pretty drawing.