What defines high frequency?
If I trade 1 hour before you, is that ok?
How about 1 minute? 1 Second? Millisecond? Nanosecond?
You don’t get it. There computers are set up to “PEEK” before the other peoples trades are ever actually executed. And then after they peek then they can still place a trade before you that is based on what your trade is going to be.
It is no Different than in poker when you have a way to see the other guys cards before you place your bet.
Currently? A trade decision (based on some kind of running average or other algo) is made in microseconds.
My #8 here is a good start for your question.