When is a slow app actually a problem?
I build Lumorem, a tool that finds what makes apps slow and sorts it by how much it hurts the people using them. Sorting like that meant digging into the research on how humans experience waiting. What it says is simple, and it explains a lot of everyday life with a phone.
Your brain has speed limits
A wait doesn't hurt in proportion to its length. It hurts when it crosses one of three lines that research keeps finding, decade after decade:
0s
feels instant, like a light switch
0.1s
you see it, you don't mind
1s
now you're waiting, your mind drifts
10s
you've opened another app
That's why making something fast can go completely unnoticed: a wait that shrinks but stays inside the same zone changes nothing in how it feels.
The same wait, in two different places
PAY
... 2 seconds
expensive
it stands between you and the one thing you came to do
Notifications
Language
EN ›
Dark mode
... 2 seconds
a shrug
you're here once a month, nobody's rushing
Identical delay, completely different cost. What makes a wait expensive is standing between someone and the thing they came for.
The same wait, for two different people
how much the same 2-second wait costs
uses the app once a week
uses it all day, for work
waits in front of customers
A 2025 study even measured people slowing down their own gestures after an app kept them waiting, as if bracing for the next delay. On a tool someone uses all day, a wait keeps costing after it's over.
A wait shrinks when you can watch the work
Researchers ran an experiment with a travel search site: when the screen showed what was being searched ("checking airlines... comparing fares..."), people rated the site higher. Some preferred the slower version over an instant one, and trusted its results more.
frozen screen
the clock says
3s
it feels like
is it broken?
"comparing 200 fares..."
the clock says
3s
it feels like
it's working for me
It's the delivery app showing the courier moving on a map. The wait didn't change. The experience did.
But you can't animate everything away
The trick only works when you'd wait anyway: the result is worth it, and nobody is timing you.
a 3-second wait
worth it, and nobody's timing you?
show the work
trying on clothes virtually: a progress bar is honest
someone is being timed?
make it fast
taking orders during the dinner rush: no animation helps
The same slowness can call for two different repairs, and picking the right one starts with everything above: how long, where, for whom.
The point
The same three seconds can be invisible in one app and fatal in another. Milliseconds are easy to measure; whether they matter is a question about people. That question is the one Lumorem is built to answer, and the technical version, with the research behind each piece, is in Building Lumorem's impact score.