The most common mistakes people make when trading US stocks

The most common scenario is that when prices rise, they say they’re doing short-term trades and want to make quick money.
After prices fall, they refuse to cut losses, and then change their story to say they’re a long-term investor.
This isn’t investing—it’s self-soothing after getting stuck.
There’s another case: you originally bought a long-term, high-quality company, but once it drops 5% in a day and 10% in a week, you start panicking and selling to cut losses. Managing long-term positions with short-term emotions is also very hard to make money.
Before placing an order, you must answer three questions
How long are you planning to hold this money?
A few days, a few months, or a few years—
Why buy?
Is it a technical breakout, an event catalyst, inflows of capital, or long-term fundamentals?
What situation proves that I’m wrong?
Trading looks at price and structure; investing looks at fundamentals and valuation.
If you can’t answer, don’t buy for now.
The most practical approach is to separate your account and positions directly:
Trading account: fast in, fast out; you must cut losses; when catalysts play out, reduce position size.
Investing account: low-frequency operations; build positions in batches; accept normal volatility.
Cash account: wait for genuinely favorable opportunities—not for the sake of trading.
Trading is: leave when you discover you were wrong; investing is: hold as long as the company hasn’t changed. The most dangerous thing is to use investing to cover up trading failure, and to let trading emotions ruin long-term investing.
My investing account is one I won’t open for the long term. The trading account is separate, and they don’t affect each other.