Investment decisions about an uncertain project are a difficult task. A decision maker can use calculation techniques such as net present value or real option. The accuracy of the technique employed can provide a significant modification to the final decision. Each of these techniques makes the assumption that the decision maker acts in a neutral way without any cognitive bias, such as overconfidence in his or her opinion. Much research in behavioural finance show that pessimistic or optimistic feelings of the decision maker can potentially lead to wrong decisions. We explore the relation of some decision biases and the use of evaluation techniques. By employing simulations, we show that the choices of a specific technique can emphasise or reduce decision bias and investment errors.