This is about differences, similarities and assimilations of various kinds of sounds [s] and [S], in languages like French, German, English, Dutch, Russian and Arabic.
In some languages, like English and Dutch, the sound [S] and the combination of [s] and [j] have something to do with each other. In most other languages, like French and Russian, there is no connexion at all.
The [S] in English in the word "sure" is there because there first was an s,
followed by a "long" u which happened to sound as [ju:]. In "nature", the t now
sounds as the ch in church, due to this same long u, even though it itself went
from [ju:] to [j@].
In Dutch, there is no real /S/ phoneme except in loan-words. We do have words like sjouwen and sjorren, but they are loans from Frisian. The only case where a real /S/ has developed or is developing, is where the diminutive suffix "je" is used with words ending in -s: haasje (little hare), huisje (small house), meisje (girl; but this word did not develop from meis + je!) and many more.
In French however, a [j] that meets an [s] or [z] in no way
changes it to anything resembling an [S] or [Z]:
Les jeux (the games; [leZ2]) sounds nowhere near les yeux (the eyes; [lezj2]). The ch in capuchon is completely distinct from the [sj] in nation.
In Portuguese ciências [sje~sj3S], the first two [sj] combinations are different from the final [S].
Russian has a systematic distinction between "soft" palatalised and "hard" non-palatalised consonants. It's a feature it shares with Irish Gaelic, by the way. A Russian palatalised [s_j] has nothing to do with an [S]. What's more, Russian even has a non-palatalised [S], and a palatalised [S_j]. So there are four different sounds. This palatalised [S_j] occurs in the former president's name Xrushchov (Хрущёв). As the spelling implies, this sound may be the result of assimilation between the ch, which is "soft" by nature, and the sh, which is normally "hard". If so, Хрущёв could be thought of as the result of a hypothetical Хрушчёв.
Dutch, and to a lesser degree English too, has a much weaker, less dark kind of [S] than the languages which do clearly distinguish between [S] and [sj]. Perhaps this is not a coincidence. Cf. Dutch sjouwen (carry, often with difficulty and on one's back), German schauen (look), and English shower.
So much for [S]. There are some strange differences between [s]'s in various
languages too. Of course, there's the
Castilian Spanish [s]. It may be that
the phonetic terms dorsal and apical have something
to do with this, but I don't know exactly what.
In French too (not Canadian French) many use a rather special kind of s. I suspect there is a phonetic similarity between this and the Arabic emphatic s (example: فصيح faṣīḥ = pure, good Arabic), which in that language, unlike French, has a non-emphatic counterpart (example: فسيح fasīḥ = wide, spacious).
The phonetic effect of the Arabic emphatic sounds is probably achieved by pharyngalisation and/or velarisation. Could it be that this French s too, is velarised, that is, the tongue behind the point where the hissing is made, is held a little higher than in other languages? I think French speakers who use this s also apply the same effect to their uvular r, or perhaps even apply it continuously, as an overall feature of the language?
Sample validity disclaimer: Dutch is my native tongue, my English and German are bearable, but I hardly speak French, Spanish or Portuguese, and no Russian or Arabic at all. So I hope the samples are accurate enough to illustrate my point, but admittedly they were not done by a native speaker.