When contemplating between working on projects with low chance of success or working on ones with high chance of success. Most people favor the latter. But, projects with high chance of success are already teeming the world. The ubiquity makes the reward not that great.
That does not mean you shall dismiss projects with a high success rate. Quick wins build momentums and increase confidence to do more difficult work.
On the other hand, projects with low chance of success turn people away. The scarcity makes it valuable and highly rewarding when it is completed successfully.
Mix your portfolio with the combination of projects with high and low success rate.