Long-term investing is an investment strategy where a position is taken in a stock, a market, a currency, or a commodity and is not sold for at least a few years. Proponents of long-term investing believe this buy-and-hold pattern will pay off in the long run.
The danger with long-term investing is staying with a position that continues to lose money. The most important aspect of long-term investing is to evaluate the investment thesis constantly. Things change. If the change alters the investment thesis, then an investor needs to sell and move on. If the thesis still works, then the difficult part is staying with a losing position until the market turns and proves the thesis right.