It appears President Donald Trump is blaming the stock market (as its own entity) for working against him. In the same tweet, Trump also appears to be attempting to upsell the market to market participants based on lots of 'good news'. The best assumption is to presume Trump is always lying.
President Trump said traders selling stocks are making a "big mistake" on Wednesday, his first comments about the wild gyrations in markets that have cut into stock market gains in his presidency. Trump said the economy is strong, and those trading stocks will regret their actions.