I was in a similar position last year, and ended up crashing and burning. I was working on a startup with two friends, and we had lots of ideas in a variety of areas (not all software). In the end, we decided to develop a "quick and simple" website to learn a bit about how to work together. None of us thought the website would make money, but that was OK because it was only supposed to take a few weeks. In the end, we wasted about 9 months on it before we finally decided to go our separate ways.

I'm not sure this helps you much with your situation. In retrospect we should have spent the time doing market research on some of our other ideas which might have been more commercial. Perhaps this is something you can do with your pals? Follow Steve Blank's advice from "Four Steps to the Epiphany" and start talking to your potential customers before you do much serious product development.

While I agree with steventruong that no-one can predict what will make money, there are psychological factors to consider: if you really think the idea is a waste of time, you won't fully commit to it and that might make it more likely to fail...

Here's how Apple solved this problem:

"Paired Design Meetings

This was really interesting. Every week, the teams have two meetings. One in which to brainstorm, to forget about constraints and think freely. As Lopp put it: to "go crazy". Then they also hold a production meeting, an entirely separate but equally regular meeting which is the other's antithesis. Here, the designers and engineers are required to nail everything down, to work out how this crazy idea might actually work. This process and organization continues throughout the development of any app, though of course the balance shifts as the app progresses. But keeping an option for creative thought even at a late stage is really smart."

http://www.businessweek.com/the_thread/techbeat/archives/200...

Say you have doubts, and that you want to discuss them. Then discuss them, in an orderly and dispassionate way. Keep in mind the possibility that you are the one who's wrong, and you'll be fine. Be calm, rational and modest.

Also: creativity does not mean not rejecting ideas. Creativity involves rejecting vast quantities of ideas. It just also involves creating more ideas than you reject. So one important phase of being creative is uncritically spawning vast numbers of ideas. Another important phase is critically evaluating them. Hemingway (apparently - this is potentially apocryphal) said "I write one page of masterpiece to ninety-one pages of shit. I try to throw the shit in the wastebasket."

A brainstorming meeting is not a place to offer harsh critique. I think it's okay to offer variations of an idea during a brainstorm, but not outright critique. This is a situation where you want creativity to flow. After the brainstorming, everyone needs to think critically about the ideas and have a time for debate when deciding what to execute.

So to answer your question, it depends what mode you are in. Are you still in the idea gathering phase? Then let bad ideas in. If not, then it's time for critique.

(I base these off of a talk I heard by Craig McNair Wilson, a Disney Imagineer. Here are some notes someone else took on the same topic.)

http://www.theparagon.org/archives/2006/02/03/brainstorming_...

At the risk of going against the opinions of others on here, my personal belief is no one can really predict what will succeed and what will fail. Many will argue that you can tell what makes sense and what doesn't but that's not completely true in all cases. Some ideas that seem like failures at first have gone on to be great successes. Sure, in hindsight its easy for many to say its obvious but most are just full of shit and they don't even realize it. Even those involved in some ideas admit they weren't sure whether or not those ideas were crazy or not.

Often times, even some of the biggest ideas out there (and small ones too), sounds ludicrous at the start with hordes of doubters. There are also ideas that have failed, not because the concept or idea itself is bad but the execution was wrong or they took the wrong approach, bad timing, wrong features, etc... and were later found to be a success by someone else.

Some ideas may sound dumb (think pet rock) and yet end up making money or are their own success in their own right. You may think that is a one-off example but I've witness enough (and done my own fair share of ideas even I think is ridiculous) that saying you know the idea is doomed to fail is in my honest opinion a bit ignorant and arrogant.

As many have said before me, experience is both a blessing and a krytonite in that sometimes experience hinders you from trying what you think is to be a failure until someone else manages to make it a success. Experience is valuable but so is the willingness to try things even if it goes against your belief.

That said, whoever said you had to spend months developing and prototyping? You can seek the right crowd (potential users/customers) to iterate whether there is a market or not without a product and in many cases, without a prototype of any kind. If you guys always wait till you have a working MVP to determine whether or not an idea is worth building (although in some cases you absolutely need one albeit rare), then you're probably not doing things right already (especially if this is a common topic that comes up amongst yourselves).

"Reductio ad absurdum". Keep asking about the details till either you no longer think it's stupid, or they see some downsides to it.

That would work if people weren't so stubborn LOL. Some people admit the flaws but still want to steamroll ahead which isn't always bad)