Hi Miguel,
Amazing questions! 😀
Regarding the stock sentiment influencing the company business, I think the majority of the customers never look at the stock performance unless the stock is doing extremely badly because the company is on the verge of bankruptcy. But then, in that case, the lack of trust in the brand comes from bad management or big market shifts.
If the fundamentals change, I could let it go. For example, If the management significantly changes and you no longer trust it, or market conditions drastically change or AI is going to disrupt that business.
Other than that, I would hold the investment for a few years, until there's no more room to grow or you believe that we are close to a peak of a bull market.
For crypto I'd ask: am I investing in this crypto because of good fundamentals or is it more about the narrative/hype? For example, BTC and ETH might actually have good fundamentals, but gaming coins are probably more about narrative/hype.