Knowing when rallies are sustainable is critical to any investor's portfolio, so CNBC's Jim Cramer looked back on his decades of experience to pinpoint exactly what makes a rally trustworthy.
And while a rally in financial, technology and transportation stocks can often signal a good rally, investors should never want to see certain stocks leading the charts, Cramer contended.
"I'm thinking about really good companies [like] the stock[s] of Clorox, Procter & Gamble, Coca-Cola, Kraft Heinz. We want those to go down because the economy's strengthening. Who wants to be in those stocks if things are really getting better? Not me and not you," Cramer said. "Look, a diversified portfolio is never a bad thing. [It's] fine to have one or two of them, but not if you expect the economy to roar, which is what the bank stock rally says."