How does a team leader refuse to allow earlier setbacks to affect future situations?

Always turn negatives in to a positive I believe. So long as ground work is made up then impact of setbacks shouldn't be so much of an issue so long as the correct changes and methods are used and implemented to move forward. Interaction, communication and motivation is key to this. Any negative issues and concerns arising as a result should be addressed swiftly and efficiently to avoid negativity or future problems. Also boosting of morale to help tackle the situation is a must, creating a positive vibe.