Taking some risk has benefits in innovation if you can afford it, but the project shouldn't have two major unkowns that can wildly affect its result.
I'm going to tweet this. Upvoted.
In addition to that, parent's advice is also crucial for the team's motivation.
If the project is boring and you choose a boring tech stack to go, the team morale will only be harder to keep up as the time flies by.
This is probably the most important reason. Programmers love challenges. Keeping it interesting/challenging will also keep your good developers from looking for other jobs.