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The stock market rose more than 400 points Monday after Europe announced a $1 trillion rescue plan.

"Investors reacted to that big bailout package coming out of Europe ... to make sure the debt crisis in Europe stays contained... Investors saw this is as a real commitment that this would not spread throughout the world and they brought stocks in a big way today."

But many are wondering whether the bailout will actually work. A stock expert tells ABC News investors should stay cautious.

"This is great news but we're trading up like we caught the biggest fish in the world. But a fresh fish today come Friday is going to be stinky."

And a writer for Daily Markets says while Monday's stock market rally is good news, it also has an adverse effect.

"What is worrisome about this...is that there’s this sentiment of 'hope' in the market. This starts to raise the question whether this move is sustainable. If you look at the currency markets, you may be questioning this move."

Meanwhile, a business correspondent on CNN says eased anxiety among investors will only last as long as Europe's financial crisis is controlled.

"...Investors mainly want stability at this point and I think they want to make sure that there is not something that starts to look like a run over in Europe. That's hard to predict. If these other countries, you know, the Greece situation is under control for now. But the real concern is whether it goes to these other countries. I think it will be kind of a slow-motion evolution until all the sudden something can happen."

So, will Europe's rescue plan have a lasting effect? Or is it creating a false sense of hope?