So I'm looking at the tutorials hoping to find new and interesting ways to do the more difficult black and whites. I'm ok at them, but it feels like I could be better. (and before anyone says anything, yes, it took me 4.5 years and ~18,000 solved to look at the tutorials. i'm obviously a male.)

All three of those tutorials felt like they were saying 'Let's try this... nope, can't work.' or 'Let's try this or this and see what might be alike'. Doesn't anything that says 'Let's try this' = trial and error = guessing? Because if not I won't feel so bad about using those sorts of techniques.

Also, if this question goes somewhere else, go ahead and move it.

I am not sure what you are asking but I'll try to give an answer.

I don't believe there is a consensus among the community regarding the connotations of words we often "hear" on these forums or in comments. To me, when there is mention of the word "guessing," it implies that a puzzler had to use absolutely no logic in placing a clue or part of a clue. The puzzler looked at the clue number, placed it in the row/column/etc., and leaves it to lady luck to hope there is no future conflicting clue.

When puzzles reach a point where there is no apparent next move, advanced technique/complex logic like MLS must be used. It is more of an assumptive approach meaning you are essentially making a temporary guess to deduce whether or not an error or advancement can be made. If no error occurs, then it means a possiblity and you must try elsewhere. If you can ascertain that the assumption does not work, then usually it ends up allowing one to place background or some other color. If one finds that using advanced technique results in no significant advancement, then one probably isn't using the technique correctly. Almost all advanced techniques require some mode of assumption, but it always requires logical deduction.

Sometimes it is arduous and time consuming but I for one would rather be certain that I can advance correctly than leave potential errors riddled in the puzzle as I progress. It takes an extremely talented puzzler to simply guess and if a mistake arises, actually be able to know how to fix it. This skill takes a lot of experience.

I hope I answered you or at least made some sense.

Logic has as much to do with finding where a clue can fit as finding where it cannot fit.
For me guessing is when I assume that something goes in a giving place using intuition instead of logic like in doing a star or the wheels of a car.
When using MLS I am looking mainly for reasons why a certain clue cannot fit in a given spot thus reducing the possibilities where it can fit. It is a slow and arduous process but will eventually pull you through.

There are often patterns in the numbers. They're most obvious on longer thinner objects, rather than (non-simplistic) blobby objects. With multiline solving, you can look at the patterns of numbers and see where a 4 in one direction is composed of a 1, 2, 3 and 5 in the other direction, and can see where the partial lines above are completed by the numbers next to the 4. This isn't intuition or guessing, or else I'm psychic. The more reasonable explanation is that the patterns I think I see are real. Once in awhile I'll follow the wrong string of numbers and make a mistake, but I mostly do large multis, and do puzzle after puzzle with the patterns working out just as I expect them to. That is, many a point value in the millions is dead easy for me because I'm following the patterns, but hard for the algorithm because it can't see them.

That said, my least favorite kinds of puzzles are complex 3 color and blobby two color (i.e., B&W). Simpler 3 color can still be solved by inspection and number patterns. The complex ones mostly only come together (at least for me) with marking out the places where one of the colors logically could not be until the only open areas just fit the numbers. Some people love these for the challenge, but I find them annoying because I want a puzzle to relax with, not to have to think deep thoughts about. The blobbly two color ones also don't have any recognizable patterns, or not enough, so one has to count out each line and move back and forth like the compiling algorithm does. That's not hard, but I don't find it fun. You can do higher order MLS on them, where you do a meta-analysis of the puzzle and put stops in the logical holes, but again, not restful.

In the really really hard ones of both these types (i.e., especially hard rather than just annoying), the only way I've found to solve them is through elimination of possibilities. That might be what was looking like guessing to you. It's not so much guessing, as assembling the possible and impossible then trimming away all the ones that don't work out as you add more information to your matrix. That's still logic, not guessing, but, in a way, you do have to assemble all the positive and negative guesses in order to make your decision tree that leads you to the right answer. Really really not restful!!

Try an 8 color multi. You'll see better, maybe, how MLS works by logic rather than guessing.

It's very simple.

Guessing means taking move you can't be 100% sure is correct. Mostly people guessing rely on probability or what is obvious (like human, you expect him to have 2 legs, or wheels, you expect it to be circular). But it doesn't have to be. That's still guessing.

With MLS, you're 100% sure.

Difference between SLS & MLS is just that you use other lines to exclude some options you are not sure about with SLS. Principal is same, you just take wider picture with MLS.

You take it from your perspective as it look to you as "trying all options", but many skilled and talented solvers just visualize it in brain.

For example, I can visualize Gomoku board in my head. When I was young, I could visualize the game so well, I could plan up to 15 moves upfront with several directions game could "go".
I play unflagged Minesweeper with 150+ clicks below 60 seconds, uncovering 381 tiles (480 - 99). Because I can click in a row because I have ~100 tiles around mouse pointer in L1 cache

My comments are somewhat similar to those of shuwix.

Guessing is anything where you are not 100% certain that it is correct.  Any logical basis that provides certainty is not guessing. That basis may be SLS, MLS or at times by an elimination method, but in every case, you work a method until you are left with a result that must be correct.

Guessing can be a wide range of things.  It may be based on an expected shape, such as the much-abused sail boats.  The reason some people love these is that they are very easy to guess for big points.  But just try doing one by any logical means, without guessing, and you will see why the points are there.  I suspect that rarely happens with boats.

Guessing may be a hunch based on some other type of expectation, usually relating to shape recognition.  I often solve puzzles where it is very obvious where a pixel should go by shape recognition, but as I avoid guessing at all costs (hence my average times), I never do that.  In every instance I can think of, the pixel has ended up the colour I expected it to be, but only after I have arrived there logically, sometimes much later after a lengthy route.

Or guesses may be nothing more than hunches, or even acts of desperation.

It ultimately comes down to why you do these puzzles.  If your goal is to top the 'top solvers' list, you may not care how you do it.  But I think there is a large section of the community for whom 'solving integrity', as I think of it, is important.

The reason people react to claims that guessing is necessary is that, by very definition, it isn't.  The validation process ensures that.  Some of us prefer that commentators understand the nature of guessing before using that word.  I understand that there is an issue of semantics here, but if we can agree that guessing means that you do not have 100% certainty of the result, regardless of how you achieve that certainty, then that may be helpful.

jock