You can't "prove" anything about businesses until they either finally fail or finally succeed (whatever your definition of failure or success is).
However, you can get a pretty decent idea of how successful an idea will be if you push it further without spending anything like 2 years on it. Most ideas that are invalidated after 2 years of the founders working their bollocks off on the business could have been invalidated much sooner than that.
Ask experienced entrepreneurs (who have built profitable businesses) around you. I think you'll find that most of them already do this to some extent - they don't commit fully into an idea until they've tested the waters and found that this idea is worth committing into.
However, you can get a pretty decent idea of how successful an idea will be if you push it further without spending anything like 2 years on it. Most ideas that are invalidated after 2 years of the founders working their bollocks off on the business could have been invalidated much sooner than that.
Ask experienced entrepreneurs (who have built profitable businesses) around you. I think you'll find that most of them already do this to some extent - they don't commit fully into an idea until they've tested the waters and found that this idea is worth committing into.