There are so many different reasons for starting a project or a business, but I would suggest two of the key considerations that we should have are:
Is it possible?
Is it important?
By possible I simply mean are we breaking the laws of people or physics? If not then something is possible (many times even if you’re breaking the laws of people things can still be possible)!
By important I mean is the idea important to a group of people? It can be important to humanity as a whole (a new type of energy generation for example) or simply important to a small group (the people in the village who are cray about speciality coffee).
In my experience if you can meet these two criteria you’re already onto a winning project. Elon Musk chooses to work on projects important to humanity, but his “possible” is wider than most given he has quite a decent amount of capital to play with. Us mere morals can also aim for these projects, but often need to scale back out scope based on the possible available!