Strokes are generally thinned at oblique intersections.
Otherwise, the joint becomes enlarged, and ends up looking bigger than it really is, due to "bleed"
Bleed is of several kinds.

Firstly, it is a traditional artefact of print typography, because these sharp crevasses are apt to fill in with ink.
Hence the preemptive move of thinning the stroke(s), and even taking it further and enlarging the pit as an "ink trap".

Secondly, there is a visual bleed in the perceptual process, because the apex of the joint is beyond the threshold of acuity.

Thirdly there is categorical or conceptual bleed, which is further up the perceptual chain; this occurs because at a joint there is a wider distance of solid than either of the stroke widths that comprise it, and this does not appear to be aligned with either stroke-- it "reads" as a blot or hot spot, visual noise which serves no purpose.

That third kind is more what happens at the bottom of the "a".

Letter forms also suffer shrinkage as well as bleed, at the outside of corners.
Or perhaps that could be described as a kind of "negative" bleed, of the surrounding ground into the figure.
The serif is the most obvious method of dealing with shrinkage, but in phototypography, "ticks" were sometimes added to corners to prevent the arris from becoming rounded. Even in a sans, the end of a stroke is often widened and sharpened, as at the top left of the "a" above, to counteract shrinkage.

Alex, in drawing every letter, it is necessary to make it physically uneven in various ways in order to make it look visually balanced. Briem's web site on letters has a nice series of illustrations of this, including thinning of joins.

That letter a in your example is chock full of really bad curves.

James M

It also might help to think of this as branching like a tree, rather than overlapping like merging road lanes.

...branching like a tree...

Not really, because the branch is thickest where it joins the trunk.

@Nick - thank you very much.

> ... the apex of the joint is beyond the threshold of acuity.
This sentence gotta have more information per bit of storage that a jpeg file :)

@William - very useful link, thank you. I knew some of the items on Briem's list, but I really like how his way of summarizing them.

@James - can you elaborate? I don't even know what to start squinting at.

@Craig - it would still imply some sort of simple geometrical relation between the curves, the one that is not there :)

@James - can you elaborate? I don't even know what to start squinting at.

I know you weren’t asking me, but the problems are unsightly bulges and bad relationships between the two sides of the strokes that create an overall lack of continuity. That a looks more like a collection of digital curves bolted together than a series of continuous strokes.

Hm. I'm just thinking that since the stroke needs to vary in thickness when it changes direction, that will create a bulge-like structures in it.

Can you point the bulges out? Or rather - let me try to:

Close, no?

Don't only look at the "strokes" as "strokes", also look at the curves themselves and the shapes they enclose.
For instance, does this shape look harmonious to you? How the curve develops?

Hm... I am guessing I will be saying "Hm" a lot now.

> I'd be spilling some of my coffee somewhere...

But it can't all be smooth with a curvature capped at some safe value, can it? Though I think I see what you mean regarding the bottom left. Is this better? -

>>>Is this better?<<<

No. It is not about "safe" it is about flow, harmony and tension.

Besides those highlighted already, there is another unsightly curve at the 7:30 position as well.

“Visual Bleed” is a nice term.

Not the straight angle that attracts me, nor straight, hard, inflexible, created by man. What attracts me is the free and sensual curve, the curves that find in the mountains of my country, in the course of its winding rivers, the sea waves, the body of the woman preferred. Curves is done throughout the universe, the universe of Einstein's curved.

Oscar Niemeyer