For example BTC is trading at 8000$ and I put up a sell order at 9000$, most times this won't happen in an instant, sometimes you wake up the next day and your order became successful isn't it? Now for those saying 'don't leave your coins on exchanges' how do you trade?
The answer is VERY simple. Make use of a DEX like the Blocknet DX platform.
You don't need to transfer your coins anywhere, you're in complete control of your own private keys at all times. You can make both buy orders and sell orders without risking your security.
It's THIS easy, yet the vast majority of people refuse to even try it.