Words to say when you don't want to speak about it otherwise it might come true

How do you say a situation wherein you are thinking of something negative while not speaking about it otherwise it might come true.

Conversely, it could also be a situation wherein you are not verbalizing a hopeful thought fearing the positive situation might reverse.

Solution 1:

The second one would be "I don't want to jinx it", but I don't think it applies to the first situation.

Solution 2:

I can't think of an expression for remaining silent out of fear of something happening if you were to actually express a thought.

It could be an example of superstition, but that's not very specific.

The closest thing I could think of—and which is more appropriate for the title of this question rather than its detail—is the phrase knock on wood:

[Oxford]

North American

Said in order to prevent a confident statement from bringing bad luck.

‘I have never, knock on wood, been typecast’
‘I used direct deposit, it hasn't been a problem as of yet, knock on wood.’

This is contrasted to touch wood, which is the UK version and has the same meaning:

[Oxford]

British

Said in order to prevent a confident statement from bringing bad luck.

‘I haven't been banned yet, touch wood’
‘We haven't had a fatal accident in the village yet, touch wood, but we don't want to sit back and wait for that to happen.’

Solution 3:

The 1st situation can be described as trying to avoid a self-fulfilling prophecy: something that you cause to happen by saying and expecting that it will happen.

The 2nd situation, as user Pantera Onca already answered, is commonly referred to as a jinx.