Editor’s note: This is a guest post by Lasse Clausen, co-founder and CEO of FOUNDD, a Berlin based discovery engine. You can follow him on Twitter here. This post originally appeared on his blog.

I just installed Pocket on my iPad. It’s well designed product that takes you elegantly through a complicated setup process.

But one fundamental step was flawed. Enough so that I’m writing this post so that hopefully in the future more product designers will save more people from this experience and have more returning users as a result.

For those of you who don’t know Pocket: It’s a service that lets you save something from the web so you can read it later on your iPad, for example. An integral part of the setup process is that you sign in the Pocket app on a device other than the one you signed up with.

When I wanted to sign in on the iPad, I was presented with the following screen asking me for my username and password:

tumblr inline mqc3z4n64I1qz4rgp A simple tip to keep your users happy when they log into your app

As always I entered my email address and password but got the following error message:

tumblr inline mqc3zuj27I1qz4rgp A simple tip to keep your users happy when they log into your app

I tried again a few times before I clicked the “Forgot your password option?”. By then I was already a little frustrated (first world problems, I know). In the forgot password option I had to type in my email address again (which by now was the 4th or 5th time).

Afterwards I had to go to my email inbox to look at the forgot password email. Among plenty of text I saw, by coincidence and in brackets, that I had a username that was a text name:

tumblr inline mqc40nTFJI1qz4rgp A simple tip to keep your users happy when they log into your app

Before clicking the reset link I tried to sign in with that username and voila: I was in.

Note that the error message above doesn’t mention anything about not logging in with an email address.

Product designers: Don’t keep me from signing in with my email address. It’s unique, I keep it all my life and I can always remember it. Usernames, on the other hand, I have many. Because many people with my name sign up for services before I do. And then I end up with a username like lasse_clausen7483. I can’t remember that.

Letting users sign in with their email address as well as an username is a very easy yet effective way to increase your retention.

I’m a geek and I put effort into using digital products, so I didn’t give up that easily. But countless times have I seen non-geeks shrug their shoulders and put an app aside after one failed login attempt. Which means that they’re not coming back to use your service again.

Image credit: Thinkstock