What’s the #1 tip that’s helped you invest and at what point did you find it?

Young-ish investor here, still early in my journey and figuring things out as I go. Currently building my habits and trying to stick to my simple rules for now:

1. ⁠Only buy things I’m confident I can hold for years
2. ⁠Hold it for years
3. ⁠Buying is allowed
4. ⁠Selling is not allowed