This seems to be related to the traditions around the "evil eye", which is a belief common to the Mediterranean world and beyond. It has varied tremendously across time and space. It's a very old tradition, very widely spread, and very much alive today. In all honesty, it's something that's probably better covered by old-school (pre-critical theory) anthropologists than historians. The basic idea is that certain people saying (or thinking) good things actually translates into bad outcomes in the future. There are two main mechanisms I've encountered in various (there may be more): one is the idea of hubris, and such "bragging" of ones good fortune will only make God/the gods/fortuna reverse your blessings to "put you in your place", as it were. The other idea is that other people give you the evil eye. In many countries, in my experience with Turkey, one must be careful not to compliment someone to strongly, or else it's a sign of your jealousy and ill wishes, and these jealous ill wishes of others will be manifested into reality. There are ways to manage this. When deal with good fortune or complimenting someone else--especially someone's young child--it is very common in Muslim-majority countries to go "Mash'Allah," because if you credit it to God, you can't possibly be jealous of the other person and therefore can't possibly be wishing them ill. Also, in many cultures throughout the world, saying something has a power that just thinking it does not, but in some places the evil eye (especially the jealous evil eye) can be transmitted just by willing it. However, I'll add that our idea of "jinx" (especially in the hubris sense) can be done without ever saying anything allowed--"Oh man, I jinxed myself by expecting to get the job."

In some places, to wish evil on someone is better than to wish good on them (as a way of winking past the danger of giving them the evil eye). In the English speaking world, "break a leg" as a well wish started in the theater world where "good luck" was seen as a potential bringer of bad luck, because of the evil eye. Therefore, the logic goes, if good wishes could bring ill, then bad wishes ought to bring good. This is said to have started in the theater world and spread to the broader English speaking world, though certainly most people who use the phrase do not consider the specific kind of evil-eye logic behind it. In the Yiddish speaking world, these maledictions could come true, so it was common to see them rescinded at the last minute--"That he should become a rich man and then have to give it all away to doctors...I wouldn't wish on my worst enemy." Or strange curses that look, on the surface level, like blessings, "May his bones be broken as often as the ten commandments" or "A young child should be named after him" (in Ashkenazi Jewish tradition, children are not named after living relatives). Of course, there were also straight up curses that people used--one of the perennial favorites is, "A hundred houses shall he have, in every house a hundred rooms and in every room twenty beds, and a delirious fever should drive him from bed to bed." But I'm distracted, we're talking about avoiding well wishes, not ill wishes.

The point is, these things are surprisingly ancient. We see a Hadith from Muhammed that "the evil eye is real." It's mentioned in the Talmud as well. We think we have found items in Pompeii that were meant to ward off the evil eye. The actual logic behind these believes goes back as far as we can go (or at least, as far as I have ever gone, though perhaps someone can tell me if Egypt and Mesopotamia have signs of the evil eye).

The point is also, these things are surprisingly recent. While the logic is old, the actual signs can be quite recent. /u/itsallfolklore argues in this thread that "knock wood" can only be dated to the 20th century, not before, though in the thread others suggest this sign may be far older. The word "jinx" can also only be dated to the 20th century, though it is again related to older precedents. With "jinx", you can see both of the evil eye logics mentioned above--both "I don't want to jinx myself" by thinking too many good thoughts, and "You jinxed me" by doubting that this good thing would happen. Break a leg, in English at least, seems to also only have been recorded in the 20th Century.

I think this old discussion from /u/itsallfolklore, while it isn't for the most part about these sorts of evil eye customs and habits and beliefs, it is still useful to think about how folklore and the larger folkways have continued into our rationalized, secularized, enlightened present. He explains it better than I could.