Pitch Accent

In Finnish, the tone is always going down. You speak at the highest pitch at the beginning of a word or a sentence and keep going down from there. That's why a lot of the times when you listen to Finnish, at the end of a sentence, you can only hear mumbling, because they have ran out of lower tone for the words. Stressing accompanies tone, so the tone also starts high and ends low.

In languages such as English, the stressing of syllables are fixed. There are some special stressing rules for the sentences, for example the pitch goes down at the end of a wh-question and goes up at the end of a how-question.

Vietnamese, Chinese, and Thai all have a very rigid sound profile. I only know Vietnamese so I'll talk about it only. Vietnamese word tones are fixed, since different tones means different words. One interesting thing is Vietnamese only has one syllable for every word, so every word is stressed. Hence, you can only speak Vietnamese in one specific tone and stressing.

In Japanese, the words doesn't grammatically have stressing syllables. However, when people stress them in certain ways to make it easier to speak. Japanese syllables are pretty hard to pronounce. You have to exercise many different muscle groups to control your jaw, lips, teeth, and tongue. Making the syllable sound higher or lower than normal may help. For example, try pronouncing 大丈夫（だいじょうぶ）stressing in different parts. The easiest way to pronounce is to raise accent at 「い」. Raising 「い」tone just conveniently put your mouth in a place so that it can pronounce「じょ」much easier. Also, a lot of this is also how a lot of people are doing so it became the correct way. There are no written rules but a lot of implicit ones. But as people speak the language through many many years, it just kind of shape itself into how they find most comfortable conversing with it. But it might not be the same for people with other backgrounds. A lot of words don't have a grammatical root but just morph themselves into existence. A lot of old meanings behind phrases that are not one bit relevant anymore but the phrases themselves kept being used with new or shifted meanings. Japanese words also have a lot of syllables, and Japanese sentences are normally long, so the muscles need to move efficiently when speaking. Combining with the complexity of the pronunciation, speaking in Japanese is a dexterous work of the muscles.