One of the companies sponsoring the conference I attended last week was passing out ‘Wallet Ninjas’ as party favors.

The Wallet Ninja is a credit card sized piece of metal that has 18 functions including: A bottle opener, a can opener, multiple screw drivers, a cell phone stand (huh?), a box opener, and a ruler.

I’m sure that whichever company sponsored this had good intentions, but I wouldn’t be surprised to find that a few people ended up slicing their fingers off when trying to open a beer. It doesn’t do much better any of the other 17 functions.

You know what opens a bottle really well:

It’s not sexy, but it’s the best tool for the job. I’d rather have one of these than a Wallet Ninja.

Startups often make the mistake of trying to be everything to everyone because they are desperate to show any traction at all. The salesperson calls the customer to pitch A. The customer doesn’t need A, but really needs B. B is only tangentially related to A, but you rationalize that it’s only code so the team will build B to make the sale to the customer.

This becomes a slippery slope. The next customer wants C and D so of course you’ll build that. The team gets to work and does only a half-assed job building out B, C, and D because they still haven’t even finished building out A. Your customers aren’t stupid and the lack of effort shows. You end up with a bunch of mediocre products that no one will ever use.

And what about A? You know, the product you gave up your career to build because you were so passionate about it. All that time you could have spent refining it or selling A got spent building B, C, and D. Product A ends up just as half-assed as B, C, and D. You rationalized that you can get back to making it better when B, C, and D are rolled out but then there will be E, F, and G.

Having the discipline to say no to these kind of requests from potential customers is one of the single hardest parts about building a startup. It’s completely different from corporate life where profit margins allow for a lot more room for experimentation and failure.

All the great startups of the past few years have become successful because they first focused on being the great at one thing. Dropbox syncs all your files, Uber gets you from A to B, Github hosts your source code. These business are all much more complicated now, but they started off with solving one problem incredibly well.

You should aim to do the same with your startup. Do one thing really well that your customers absolutely love and make it the best product it can be. In other words, your company’s product should be the bottle opener and not the Wallet Ninja.