You might hear experienced investors talk about the concept of a "wide moat," especially if you're reading anything about Warren Buffett's investment style. Just as a wide moat around a castle makes it difficult for enemies to invade, a company should have a "wide moat," too: a sustainable competitive advantage that will prevent competitors from stealing that company's market share.
What would make me sell: Sometimes there are good reasons to split up. For this part of your journal, compose an investing prenup that spells out what would drive you to sell the stock. We’re not talking about stock price movement, especially not short term, but fundamental changes to the business that affect its ability to grow over the long term. Some examples: The company loses a major customer, the CEO’s successor starts taking the business in a different direction, a major viable competitor emerges, or your investing thesis doesn’t pan out after a reasonable period of time.