I think many amateurs (I am one) are taken with the desire to make things, and relish the challenges of the joinery that enable them - the design is often a means to an end. I find the technical aspect more intuitive and struggle with design, hence looking at pleasing pieces is as important to me as studying techniques for well fitting joints.
It's worth noting that the things I have made for people have been liked for how they look and very little of that is due to the difficulty, or otherwise, of the joinery.
Note to self: Get better at designing.
your note to self is mine, too - what are general design cues, and then being willing to accept once you make specific items, there is another layer there.
I think that's also what people struggle with almost across the board unless they were born able to see and draw what they see and still be willing to do iterations.
I'll show something I find useful from a design sense. Most things have to have straight lines somewhere (this is a guitar example, though). Hamer made guitars in the early 1980s, and by most accounts, they are better than what gibson was making at the time.
Here is a hamer guitar from that period, and its' worth a little less than a comparable gibson now, despite the quality from gibson in 1980 not exactly being top shelf.
The black arrows aren't exactly great labeling attempts, but they point at two toxic design items. The heel of the guitar looks like a trapezoid in a sea of curves. wf is that? It's a no no.
And when you look at the back of the guitar body , the lower bout is a bit tubby (the "belly") and the two horns aren't that inspiring, but there is a toxic design error across the back the double cutaway is curves meeting a flat line that goes a great distance across the body.
Mixing curves and straight lines in a single element is unnatural looking. There may be instances where it works, but there are few of those that I can think of. The neck line itself along the sides is straight, but it's a completely different element, so it is primarily straight.
Now, a guitar designed 30 years prior somehow eluded those (gibson spent money for designers).
Notice how the curves on the body are curves - the cutaway is curved, and the only flat part is right where the neck heel meets the body (this is avoidable, but it's OK - on higher end makers like collings, they don't even abide by that, rather they make the heel fit the shape of the body instead, but collings is a better maker than gibson and their guitars are more expensive).
This is one little thing that I learned early on twice in tool handles and tool eyes. I couldn't tell why they looked bad, just that they didn't look right to me and someone who is a superb designer pointed out "that's either a curve or a straight line - not both - pick one".
In well established things (like better makes of wooden planes), the handle and the eyes are like that. more natural looking. Sometimes it seems inconvenient to incorporate the continuity of curves, but it makes a huge difference if you're not looking to take risks.
