At CMU yesterday, I heard a story about how Yahoo Trip Planner has pretty much zero adoption. It has never taken off, though it remains online even today. Yahoo keeps it around because it's fantastic for recruiting. People love to work on this idea! Yahoo recruiters lure talented engineers, designers and PMs to work on this project, then gradually shift them off to real value-creating projects once they're hired.

Travel planning software (the kind that you would use with friends and family to plan vacations) is one of the most common ideas pitched. It has been attempted, and attempted, and attempted again.

It doesn't surprise me that people go after this, though. The idea actually points in the right direction: founders pursuing this idea are looking to solve problems or pain points in their life. Brilliant. And practically everyone has the problem of not spending enough quality time with friends and family. Travel is the best and most meaningful way to do that. Surely this is something that solves a big problem that everyone wants.

Yet so far, this particular idea doesn't lead to massive success and incredible amounts of value creation. My best guess is that a truly great consumer service needs to be something that is can be used every day. My friend Suhail Doshi, CEO of Mixpanel (he'd know a thing or two about analytics), recently told me that 20% daily retention is probably the baseline at which a service has legs.

This points to the deeper problem that underlies every product or service: obscurity. I only have a finite number of slots in my brain. If I don't remember it, I won't use it. And I only remember things that I use often. Just like I order Coca Cola whenever I get a cheeseburger... the consumer web/mobile services I use need to be things I use all the time.

Which leads us back to trip planning. How often do people really plan trips? For the typical working adult, probably once or twice a year if you're lucky. In fact, Americans are notorious for shirking vacation, clocking the lowest rates of vacation on the planet. Twice a year just doesn't cut it.

I used to think nobody needs this. That's probably not true. Lots of people want this. They just won't ever be able to remember it.