First, try to make taking on challenges and self-improvement part of group culture. You can introduce your team to various books/videos/articles around people

First, try to make taking on challenges and self-improvement part of group culture. You can introduce your team to various books/videos/articles around people overcoming all sorts of challenges on a day to day basis. Such an environment motivates everyone to take on challenges: fitness, intellectual, social, and so on. It is important not to single out anyone on a particular dimension. Acknowledge that we are all lacking in one area or the other - so make it a general team thing, something super normal within your group to work on enhancing both strengths/weaknesses. As a practical step - share your own shortcomings, and how you have/are overcoming them. This sort of personal struggle, and your efforts to overcome will motivate others to share their own struggles and overcome them.