Don't fight the tape

Don't fight the tape means to not try to go against what the stock market is doing. The stock market includes all the different stocks, bonds, and other investments that people can buy. If the stock market is going up, it means that the prices of lots of these investments are getting higher. Even though you might have an opinion about a certain investment, it might be better to just go along with the stock market. If you try to go against the stock market, you might make wrong decisions and lose money.