I am down 22%, and I am not sure if I should hold conviction or admit defeat.

Not looking for sympathy, rather just looking for framework. I am down 22% YTD. These are companies I researched properly, not meme stocks, or speculation. Three of them have solid fundamentals and I still believe in the thesis. But one of them I am starting to wonder if I missed something when I bought it. The problem is I do not have a clear rule for when holding conviction through volatility ends and this was a mistake and you need to exit begins. From the inside, they feel identical. How do experienced investors tell the difference? Is it about whether the thesis has changed, or the business has changed, or the price is telling you something the fundamentals are not? Genuinely trying to build a better mental model here.