CNBC’s Jim Cramer on Thursday told investors not to approach the stock market with an overly pessimistic attitude. He gave a few examples of stocks that saw gains recently after they were “written off” by some on Wall Street.

“You can be as cynical and corrosive as you want about the vast majority of things in the world, in life,” he said. “But if you’re trying to make big money in the stock market, you’re actually better off being critical and constructive. Reflexive negativity is not a smart strategy.”

Cramer pointed to Walmart, which initially jumped on Thursday after the big box retailer reported an earnings beat. But shares fell before open when management struck a cautious tone about the impact of tariffs, he continued. Cramer said he found the loss surprising, pointing to Walmart’s strong advertising revenue stream, sheer scale and balance sheet. Walmart, he claimed, is “one of the rare companies that can cope” with the industry-wide issue of higher tariffs. He noted the stock managed to even out by close.

Too many investors doubted Disney and “gave up on all of that excellent expertise and intellectual property,”Cramer suggested. Some believed that its theme parks and offerings were too expensive, he continued. However, the stock has managed to climb, he added, and the company reported a strong quarter last week that beat estimates — thanks, in part, to better-than-expected growth in streaming subscribers.

Cramer also mentioned Nvidia, which weathered huge losses after Wall Street feared the artificial intelligence boom would go bust. But he said the stock has started to rebound over the past month as demand for the company’s products remains strong.

“If you examined these same opportunities with a jaundiced eye, too critical, too negative,” he said. “You would’ve passed on all of them. But if you were open-minded, if you were constructive, any one of these could easily have made you a boatload of money.”