You just don’t know what will happen next. It’s not just true when considering what kind of trade or position but it’s a helpful metaphor.
The important thing, I currently think, is to remember that you’re just trying to get a sense of a market (a stock, future, whatever). There’s no “predicting” there’s just guessing with some degree of probability.
There’s no need to trade anything, anytime.You’re looking for a “good” trade for the market at that time. You look at the market, watch it and learn to “feel” what’s going on. That push and pull between buyers and sellers.