I have a very hardworking team, and I like when they try to think about a project with broader perspective. I want to respect their contribution and don't like to refuse their ideas, but sometimes I know that a given idea is going to fail when executed, as per my past experience.

Executing and proving the idea, will take lot of time and resources. The idea may be good enough on paper to explain and very much convincing. But if I try to tell them that it is going to fail, and we can't use your idea for this project, then that is kind of demoralizing for them. What would be the best step in this situation?

The current scenario is:

We are working on data science project and suggestion by team member is logical and convincing if we look at it in greedy method.

Executing it will take considerable amount of time and team effort. I have suggested him to work on it side by side by taking small but stratified data sample and get output. and have suggested some checks in further stages, which I have doubt on. Here I have taken this decision because we don't want to miss out that 1% chance of my doubt being wrong. And time and effort of only one resource is being utilized on this idea which is manageable.