Getting text to display properly is a surprisingly difficult process. Back in the days of moveable type/linotype/etc. there was a human who would be involved in every step of the process, and they'd use their judgment to decide exactly how to make each page look. Things like hyphenation, line spacing, typography... were all decided by a person. Which was great for high-quality, artisanal works, but kind of sucked once you wanted to change something on the fly or alter the format of your printing.

Then came the computer. For a while, the questions of how to make a page look good were sidestepped by using very basic syntax for representing and printing text. All printing characters were the same width, and to figure out where a line break fell when printed you either used a naive approach (break anywhere in a word once you run out of space, resulting in words being spl
it right in the midd
le), or you looked to the end of each word and decided if there was enough space left in the line to print that word.

The systems we have today are partially a compromise between the primitive state of the art when the first typography standards were being decided on, and the least-worst decisions that could come out of that. My biggest gripe is the conflation of semantics and syntax, or semantics and graphemics - if you've ever witnessed a debate between programmers about whether tabs or spaces are better, you've seen the result of this. But I get ahead of myself.

Everything in computing is represented by a stream of numbers. In some cases, those numbers indicate to the computer to display something on the screen. In other cases, however, the stream contains instructions on how to display what it's displaying. And then there are the instructions that affect both.

So, in markdown, the * character can be used as an indicator of style (italics, bold) or as the asterisk character itself.

The problem I alluded to is basically a question of the role of breaks. Breaks are syntactical elements that indicate to the renderer how to handle text in an abstract manner, by treating elements between breaks as belonging to a class of objects. There are a number of breaks: line, paragraph, section, page, chapter... and, in some sense, the End-of-File character can be considered a break as well. There are also characters that indicate where breaks should not occur, such as the non-breaking space.

For arbitrary text, the proper use of this abstract model allows text to be rendered to any device and still come out conceptually pure; i.e. the same book that you can print on legal paper would look good on A4 paper, and would also look good on a mobile phone. Separating the graphemes (letters, numbers, punctuation) from the visual instructions (spaces, tabs, tables) permits a renderer to take the text and make it work on whatever it's being printed to.

In reddit comments/markdown, there is a much more limited set of tools. Comment fields are limited to something like 10k characters, so no one is going to be writing chapters or pages in here. But what about poetry? Computer code? Because one of the things I didn't mention about the different classes of breaks is how they handle formatting - notably, line breaks tend to preserve formatting, whereas paragraph breaks tend to return formatting to the default. So if a line overflows, but you want it to render as the same style as the paragraph above it, you really want a line break.

But maybe it's better if I just show you some examples.

1. Reddit does auto numbering.

2. And it tries to maintain the visual sense of the inputted text throughout numbered sections.

But if you do a paragraph break and then try to return to numbering,

1. it starts over from 1.

On the other hand

1. If you start with a number,
   insert a line break,
   and then keep going

2. it will format properly.

TL;DR: Paragraph breaks start over, line breaks keep going where you left off.