The greatest tip everyone should adhere

Stop timing the market! Take profits when you can.
The market will always fluctuate. Good things only happen when we least expect it. Just because the stock is dropping a lot doesn't mean it will rise the next day.
A lot of factors come into play. As long as you do your due diligence to research about the company, you will stay fine!
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Also, take profits when you can. Most of the time, stocks rise very high due to a sheer number of people trying to short it. After the short, the stock will start crashing. Take profits and leave. You are bound to feel disappointed when you see the stock continuing to rise but at least you know you earned.
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Lastly, if you are losing a lot in the stocks you are holding, do consider holding for long term or just reinvesting the money into growth stocks. It is always good to cut losses.
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$Tesla(TSLA.US)$
$Moderna(MRNA.US)$