What makes a person a good investor is the ability to take calculated risk and also know when to pull out ones investment. Emotions must be mastered so much that it plays little or no role in an investor making decisions (financing or investment) decisions as the case may be. Even in the case of a loss, an investor must take appraisal of the process and find out where he/she got it wrong. This is will minimise a repetition of the same mistake in the future.
Emotions must be taken out of the decision process that we take, at first this may seem easy but many times I see investors taking decisions based on their emotions instead of letting their strategy to play out and when that happens it is better to try to comprehend why this is the case.
If you do not do that then it is impossible to eliminate your emotions when you invest and if you are unable to do that then it is impossible to eliminate your mistakes which is key to become a successful investor.